Still think Wish would be the most likely, I found a really simple way to fix him,
1. use Wish to time travel back to a least a month before Balduran's transformation.
2. use disguise self so he doesn't recognize you.
3. get Balduran's hair or DNA.
4. cast clone without anyone knowing, in a location you know will still survive all these years.
5. let everything else play out like it should.
6. use Wish again and travel back to present day.
7. act surprised when you find the clone.
I mean it wouldn't change anything, besides the fact that there's now a clone body of Balduran hiding around somewhere, could be the plot of a potential DLC.
