Shockingly, I'm getting this exact same bug even today. I tried to quickload during the last boss battle and now attempting to load any of my recent quicksaves crashes the game 75% of the way through the load bar. However, loading the named save I made right at the end of Act 4 (before entering the door to the academy) works, as does the 5th quicksave made a floor below inside one of the test dungeons. Verifying the game files through steam does not fix the issue.
I have a creeping suspicion the game does something very bad when it removes the Death Knight from your party as part of the final battle, and it is unable to rectify something when loading the final level of the academy.
