[X] Yes
-[x] Prepare some contingences just in case, because those with a hunger for power will never be truly predictable...especially these "wind users" as they are...
-[x] but on the off chance, try to convert him to your side with the chance of truly becoming a immortal being, however the price of such a thing would require...service...as per a agreement (aka: Nazgul-ification, having one of our new ring-wraiths be able to summon the dead would be a wonderful thing, as well as a way to get started on useful minion projects)
I suggest this for just in case people...I mean having a necromancer would be interesting, however we need to be cautious...but if we can have him sign a agreement to only use the corpses of our enemies (aka forces of destruction) and not our own? Well then he will be tolerated and under our protection...as long as he also understands that by our service he has a way to live beyond mortal years...
However we don't tell him everything about the steep price of Nazgul-ification, just most of the benefits and the deterrents...like vulnerability to fire and spirit damage, however being able to be revived and literally require bullshit levels of epicenes to be killed or slain? hell yes, plus with our experience and this worlds magic system we could even improve our old workings on the Nazgul's themselves. This way we could get a early servant out of this mess, and if we take over the border princes to become New Mordor? Then great!!!
as this way we can eventually get Uruk-Hai (more reliable then Orcs, even if we have to rush to them), I also suggest we go on the path for Jack of Trades...while we wont master everything, we can do everything to a okay degree, and once we get all three of those realms of power under our belts? Hunker down and train our asses off until we master all three realms of power and tell the forces of chaos, destruction, and other things that threaten order and stability of the world to fuck off!!!
edit: I mean can you imagine the empire in a serious battle, and then out of nowhere a Uruk-Hai army charges from holes made by Were-Worms (aka the giant ass rock-crunching monsters that remind me of Purple Worms from DND) to tear into the armies of chaos as we fuck them over? not to mention killing off the skaven would save the world a Massive pain in the ass...especially the lizardmen should at least be thankfull they would have a chance to rest and recuperate. Hell if were lucky we can even trade with them and be acknowledged by the Slann as needed for the "Plan of the Old One's".