And I was probably a bit too broad in my description. Biff wasn’t wiped out of every timeline, just the one he set off by giving the almanac to his younger self. He didn’t return to the same 2015 that he left. He returned to the 2015 of the alternate timeline that he created. By the time that his death earlier in the timeline caught up to him, he faded out of existence because he no longer existed in that timeline. Bob Gale explained in the DVD commentary of that scene that it was deleted because there was no setup for it and audiences would be taken out of the flow of the movie if they had to ponder what happened. The scene was what he called a “showstopper.”
You’re correct, my mistake.