When Marty and Doc return to 1986 to find the "Citizen Brown timeline" and Doc disappears, shouldn't the time machine disappear as well? Since the original Doc that Marty knows ceases to exist, (the Doc that created the time machine) then the time machine should cease to exist as well... right? Because Citizen Brown is the only existing Doc, and he never build the time machine. One possible solution is that the time ripple effect doesn't reach the time machine yet. But then why did it reach Doc so fast? I'm guessing that people are affected by the ripple effect much quicker. But then, in Episode 5, Hill Valley changes almost instantly while in the 2nd movie, Hill Valley changes very slowly when Marty and Doc go back to 1985 from 2015. So the speed of the time ripple effect seems to be pretty inconsistent. Or is there some sort of set of rules?
And if the time machine would cease to exist, then shouldn't all consequences of time travel meddling cease to exist as well? I would imagine that in that instant, Marty would wake up in his room that night he went to see Doc at the Twin Pines Mall and would have no memory of the events of the films or the game. It's reminiscent of a Justice League episode when they break Chronos' belt and then they revert back to the beginning of the episode before any of the time travelling took place.
One other question: what has the Doc that appears in Episode 5 experienced? I mean, that Doc is like a completely different Doc that we know from the films and from the first episodes. Let's track his life:
Emmet continues his life, pursuing his science career. He invents the time machine and the events of the film trilogy all happen. I wasn't sure if that's true at first, but it must be since Doc is married to Clara. But because of Marty's interference with his younger self, he's closer to his father and therefore he stays in Hill Valley and earns the key to the city and doesn't go around time as often as he did as the previous version of Doc. He reads Marty's note, realizing that Michael Corleone (or whoever you named Marty as in 1931) was Marty and also (I'm guessing) realizes he shouldn't go to 1931 in August (or whenever episode 1 and 2 were) because he might get arrested. But he does go in October by instructions of the note. Is this correct?
Sorry if any of this has been mentioned already, i haven't found anything on it in these forums.