You guys would be doing this without his consent, yes? Because he prefers what he is now and didn't even want to change back for his best friend/lover.
Whose consent? In the game we are talking to Mindflayer with memories of the Baldurian. Of course he has no investment in getting Baldurian resurrected. It doesn't mean that Baldurian himself wouldn't be happy to be brought back to life.
If Balduran was completely gone, how did Ansur recognise him in the Prism?
Balduran turned into a mind flayer before he killed Ansur. We see it in the flashback that the transformation had already happened. So Ansur, being the spirit of a powerful bronze dragon, could easily be able to recognize the mental presence of the Emperor, even if he isn't familiar with mind flayers not having souls the way mortals do.
You guys would be doing this without his consent, yes? Because he prefers what he is now and didn't even want to change back for his best friend/lover.
Whose consent? In the game we are talking to Mindflayer with memories of the Baldurian. Of course he has no investment in getting Baldurian resurrected. It doesn't mean that Baldurian himself wouldn't be happy to be brought back to life.
Does anything prevent the Emperor from continuing to exist if you brought back Balduran with a wish/true res spell? I mena, you could resurrect Balduran (his body is consumed) and they could both exist provided no one tried to go after the other one.
In D&D no.
In whatever Larian fabricated, no idea. There is no internal logic to what Larian does.
The only thing that might prevent a true ressurection is the 200 year time limit. The entire timeline about the emperor is messed up, so no idea when Balduran died.
As far as I can tell, Baldur's Gate was recognized as a city by around 450 DR, while BG3 takes place around 1500 DR. When Balduran was turned or how long he lived is hard to say, but even if he lived 500 years as a human before he was turned, that'd still be 500 years ago. So if there is a 200 year limit, Balduran can't be resurrected.