The biggest reason I would consider voting to go with the Sojourner when they leave is that, by then, we'll have eliminated most local issues of a sufficient scale to warrant our continued involvement, heroically speaking, and the way things are laid out now, most of Arcana might come with us.
See, I have to dissagree with you on this. I acknowledge that such a choice would probably be the remit of a sequel, but there will still be Plenty of work to do on Earth Bet once the Endbringers are all dead, least of which will be rebuilding all the places they wrecked before that happens. The real thing would be the repercussions of Taylor introducing Magic to Earth Bet, which she would definitely feel responsible for. That alone would probably take several lifetimes at least to sort out (and with IAE pulling shenanigans it's definitely likely Taylor could live to see all of them), but also remember that Parahumans are going to keep popping up for at least another three centuries before all the shards finally run out of power, so there are still going to be new non-magic S-Class threats and other problematic craziness popping up to keep her busy.
I also don't really see Taylor and Arcana having that level of freedom in TSAB administrated space. The Administrated worlds, despite the TSAB itself mostly being a peacekeeping force, still have a very regimented and militaristic society. Even "independent" mages are very closely regulated and restricted without some sort of official mandate to say otherwise. Further, I see them taking one look at the nepotism and other corruption still present in the organization even after the elimination of the brain-jars, and the religious zealotry/revisionist history present in the Saint Church, and being quite disillusioned about any notions of the TSAB being a more "enlightened and fair" society than anything they could find on Earth Bet. Heck, I actually see Taylor being more forgiving of the Jar-Brains than the rest of the TSAB if/when she finds out about them. After all, after everything she's learned about Cauldron, while she may not agree with their ends-justify-means philosophy, she at least understands Why such actions are taken even if she doesn't want any part of it or the organizations that sanctioned it herself.
Really, I see Taylor going the Dr. Jones route once the US government reclaims monopoly of force for powers and starts to tighten restrictions on vigilantism again. Especially once Magic becomes public knowledge, she'll still be able to use most of her powers freely, so long as she doesn't do anything illegal. I see her retiring from heroing either to a job in programming with Dragon Tech, or else teaching university level mathmagics, and every once in a while the government contacts her to help deal with something the normal methods can't handle.
She might be able to find a similar position somewhere in Administrated Space, but the main difference is that Earth Bet is Her world. By then she'd have helped save it from the Endbringers and several other S-Class threats, but there's always more work to be done, and she'd be committed to making sure things on Earth Bet Keep getting better instead of slipping back into the shit-hole it was in her youth. Further, if she left for TSAB space and became a citizen there, their Prime Directive would more or less prevent her from helping her home at all since she would then be beholden to Administrates Space Law. And that's if she could even get back to Earth Bet at all considering the displacement shear cutting off the Bet-Cluster from the rest of the dimensional sea.
The TSAB is vastly less hypocritical in their version of the prime directive.
I never said that the Federation weren't a bunch of hypocrites. Just that the TSAB's prime directive takes its stance on which worlds they can contact too far.
See, the only major restriction in Star Trek's prime directive, at least as far as "Official" first contact is concerned, is that someone on a world has to have developed a method of superluminal space flight. That's it. Full stop. Heck, when Zefram Cochrane built the Phoenix, Earth was in a state of fragmented post-nuclear war societies. The other reason this makes sense for them is simple: This society is capable of superluminal travel. Sooner or later, they are going to find us, so we might as well open dialogue on our terms. The Federation also wasn't above interfering in these transitional worlds' by providing warp technology to nations that hadn't yet developed it if the nation that first did was a government they couldn't get along with. The logic there being "this world's level of science has this capability. If this nation of xenophobic imperialists doesn't use its warp-tech to wipe out these other nations we actually get along with first, they'll find a way to do it themselves within a decade or so, so it's alright to help them get a leg up so we don't have yet another enemy to deal with. The Romulans are bad enough..."
The TSAB, on the other hand, requires a world to be a homogeneous monolith society encompassing the entire world, regardless of that world's ability to traverse the Dimensional Sea. This is short sighted at best and dangerous at worst as I see things. Imagine for a moment an alternate Earth much like ours. It has all of its nations across all of its continents with all of its squabbling. The only major difference is that this version of Earth is a mid-level magic world. Now imagine that one of these nations develops magic based Extra-Dimensional travel methods, quickly followed by several others, and these nations set out in a race to expand their holdings and settle other worlds. Despite these nations controlling the entirety of these extra-dimensional worlds, since their societies began on the fragmentary Earth, the TSAB will not contact them, and may even try to cut them off from areas of the dimensional sea without alerting them. Now imagine that this development of Extra-Dimensional travel and colonial expansion didn't start in the modern era as we know it. It started in the 1940's, and the first nation to discover the existence of the TSAB isn't the Magic!United States, but Magic!Nazi Germany...
I'll just let the implications of that settle in...
Moving on to the second part, selectively ignoring it, in particular I don't agree with the poaching of powerful mages from less developed non-administrated worlds, since doing so can actively hinder that world's ability to develop their own magitech, achieve extra-dimensional travel, and benefit from the resources and opportunities it offers. Now, some people might say "but Almech, they're just one person, and it's magic, who would believe them and what can they really do⸮" My answer to that is that Nanoha magic is actually math. Science. It's consistent and repeatable, not mysterious and unknowable. Once someone gets their foot in the door a lot of the limitations you would normally expect will go away, and history is full of examples of "just one person" who changed our entire understanding of science and the universe. They'll just either have to change the name to something other than magic, or else redefine the word magic to refer to the new branch of science. It wouldn't be the first time a word had its meaning completely reversed from its original definition...
Even just giving SW an opening to show off new characters wouldn't be any less connected to story than Jujak as some are pushing for.
