#i'm sure marty's told him about it at some point and doc definitely feels bad over that

[doctorbrown]

Also, unrelated because now I'm just thinking about it—I imagine Marty fading out of existence had to be super painful. Like it's a horrifying, harrowing experience, and in the film even though the camera is only on him for a few seconds during the George / Lorraine moment, he looks incredibly pained. Which makes sense, I mean; he's probably losing his senses, his control over his body more and more as the seconds go, everything's just collapsing until that moment where there's nothing, not even a memory.

That deleted scene from pt.2 with Old Biff definitely supports that but it also looks like it insinuates that the ripples in time will catch up and effect a person based on how they're removed from the timeline. He fades out in a way that alludes to the fact that Lorraine shot him well before he could ever make it to that age.