"This granted, allow me to treat the various types of failure mode as independent, although, of course, they will be simultaneous and the second-order effects of their interplay will be complex and staggering. First, for the Gōketsu. Jiraiya would, naturally, take control as clan lord. Your rule has been mixed, shall we say, while he is a veteran statesman with a decades-long record of success. He would not be so irresponsible as to leave his people's welfare in the hands of a junior, much less place his vast power directly under your control. You would naturally lose all the agency to which you have grown accustomed, your role reduced to advisory and executive after the fashion of Noburi or myself, and I may remind you that Jiraiya was not of Uplift. He was coming to express an interest in it, in terms of benefiting Leaf by better leveraging its civilians, but he was ultimately a man in his fifties who had spent his life in a Leaf prospering under the Third's stable, moderate regime. He did not propose or conduct any bold social experiments then, and the KEI is as much his legacy as anyone's, insofar as he did not lift a finger to save his clanless brethren, for all his power and influence. I have power now, Hazō, if complex and qualified, and it leads me to respect Jiraiya less and less as I come to comprehend just how much he could have accomplished with his and did not.
"Even as I acknowledge that Jiraiya displayed some openness to new ideas, the institution of till'n'fills being his finest hour, the fact remains that the Gōketsu's Uplift drive would attenuate by orders of magnitude were he to replace you as its autocratic leader.
"Let us take a step outwards. A fierce power struggle would naturally ensue over the Hokage's seat, Jiraiya only ever having taken it in order to rescue Naruto and doubtless ecstatic to be freed of the burden, and the Seventh seeing an opportunity to transfer a duty he never pursued and likely does not feel himself equal to onto the shoulders of a much more qualified superior.
"I imagine Jiraiya would emerge victorious, with his superior skill and vastly superior experience, as well as the existing precedent of the older Hokage stepping aside for the younger. I hope you did not possess any fantasies of a loyal Hokage in office. Beyond that, Jiraiya would certainly be a grand political asset, and your odds of execution would decrease considerably, but I suspect he would wish to avoid overshadowing his mentor's son's rule, so long as that rule remained to Leaf's benefit. To repeat the comparison, he did not rule from the shadows when his own apprentice became Hokage.
"Speaking of the Hokage... I hope you appreciate that your control of the rift would last only until the first expeditionary team encountered the first human. If the rift is proved as a potential source of 'new' Leaf shinobi, or shinobi willing to be recruited to Leaf's banner, it must be under the Hokage's direct control. If it is a potential source of hostile shinobi, Kage-level at worst, it must certainly be under the Hokage's direct control. If there are other parties with whom Leaf may negotiate for advantage in an unknown world, again, you are not the person to whose judgement such weighty matters should be entrusted. I assume that from that point, any exploration would be conducted by the most trusted, competent, and, of course, discreet shinobi available to the Hokage, while you would be expected to return to your own specialisations, such as research and development.
"Meanwhile, once the existence of the rift became known to the clan heads, as it would need to be with Jiraiya's return and the regular recruitment of their members for expeditions, there would be a competition of unprecedented ferocity over who should be rescued next—for obviously Leaf's expeditionary resources are limited, and traffic to and from the site needs to be limited also. Every clan head would demand that their fallen take priority, and exert the full extent of their influence to ensure that their parents and siblings, their heroes and their masters capable of expanding the clan's temporal power, come first. Or do you believe you are the only one willing to cross lines and embrace extremes to resurrect a loved one? Needless to say, I intend to participate fully in this competition, for Leaf's clanless deserve a second life no less than anyone else—arguably more, since their first lives would on average have been shorter and worse—while the Gōketsu would be all but irrelevant with no more prominent figures of their own to rescue. The damage to Leaf's unity and stability would be... honestly, beyond my power to estimate.
"Now, let us expand our scope again to consider events in the outside world as Leaf tears itself apart. It would be impractical, realistically unviable, and counter-productive for Leaf to attempt to conceal Jiraiya's return. Much of his value is as a diplomat and as a military deterrent. Nor would it be plausible to pretend he was alive from the beginning, between the survivors' testimonies, his absence during Leaf's recent crises, and the fact that there was no conceivable reason to keep his survival secret even from the Tower's own shinobi.
"As soon as Leaf's capability for resurrection was discovered, even if Leaf itself claimed it could not be replicated, it would be swarmed with spies and with demands for explanation. Every other nation would be terrified of Leaf resurrecting more Hokage, and rightly so, I regret to say. Do you believe the existence of the rift could be concealed for long, considering that Akatsuki were present when it first opened, that it would be the focus of the greatest political struggle in Leaf's history, and that it lies far closer to Mist than to Leaf?
"The AMITY nations would naturally demand that the rift be given into common keeping as Pain's seal was, and for the same reasons. I note in passing that this would technically place it under Ami's control, since it is she who administers AMITY matters not under the purview of any given member. Alas, I do not believe this final saving throw would ever be rolled, as no Hokage or potential Hokage we know would consider surrendering the rift. The possibility of it falling into enemy hands is an existential threat, and any hands may become enemy hands when they face the temptation of conquering the world with an inexhaustible supply of loyal demigods.
"I need not belabour the point from there. The most realistic scenario is that Akatsuki would claim the rift, formally on behalf of AMITY should they desire that fig leaf, and test if Leaf can defend it in the distant land of O'Uzu. They are already aware of it, and we only assume that they have not been researching it themselves. Once it is brought to their attention that it can be used to resurrect Pain, to whom they were fanatically, and, per your speculations, in some cases romantically devoted, no power on this Path will stop them. And if you are capable of finding and retrieving Jiraiya, they are certainly capable of finding and retrieving Pain.
"I trust I do not need to explain how a returned Pain, together with control of the rift, would leave the rest of humanity at their mercy. Among other considerations, I invite you to contemplate the image of Pain sacrificing himself to resurrect any Akatsuki members we are somehow able to defeat, then strolling blithely back out of the afterlife without assistance now that the rift is open and he knows the way.
"This is still arguably the best scenario, for Akatsuki claim world peace as their objective. The alternative is for AMITY to collapse, as pre-emptive elimination of a member state due to potential threat makes mockery of its very concept. That collapse, of course, would take the form of Leaf's destruction. Needless to say, the man with the ability to manipulate the rift would share its fate—destroyed if its new masters choose to destroy it, or enslaved if they wish it under their sole control—together with any associates who might have been inducted into the same secrets, or might be needed to provide leverage in the event of resistance.
"Accuse me of pessimism if you wish, but I cannot believe that, with the rift taken from Leaf by force, the remaining villages would come to a reasonable agreement as to its ownership and use. Ami could certainly arrange it, but even assuming she survived Leaf's destruction, with AMITY failed, I doubt she would possess the credibility and influence. No, I consider it much more likely that they would return to form, and war over this precious resource until it was either destroyed or claimed by a single definitive winner. There is little point in speculating beyond that, except to say that the kind of village that would successfully trample all others for the sake of power is unlikely to then use that power in an Uplift-friendly way.
"These are the key points which capture my imagination, Hazō. If you desire others, Shikamaru and I have a bulging folder. If I may be frank, your assertion that research is proceeding smoothly terrifies me. Still, you have come to me to seek advice, and therein lies a seed of hope that you will give these issues serious consideration, and refrain from triggering this possible apocalypse until you find solutions that satisfy you and, with my aid, polish them into solutions that satisfy Leaf's finest realists as well."
Hazō sat and stared at Kei mutely. Doom-pronouncing rants were nothing new for Kei, but it was hard to evaluate their validity, since generally he took her advice and didn't do the thing, and so the disasters she predicted had no chance to ensue. Terrible as he apparently was at seeking her advice when it mattered, he prided himself on his ability to accept it when he did, even when it was intensely critical and made him feel like an idiot. He also couldn't think, off the top of his head, of any instances where accepting it actually backfired (except in terms of lost opportunities where nothing would have gone wrong, a type of counterfactual it was difficult to assess).