My thought is more along the lines of a gradual shift in his memories - when Marty was in the past, the changes he made did not impact him instantaneously. The picture of him and his siblings faded over time, until he established a future in which they could exist. He could very well 'recover' the second set of memories gradually, with the additional possibility of keeping both sets of memories intact (one hopes that either the short time spent in the Biffverse 1985 or the fact that a separate Marty still existed in that timeline would prevent him from imprinting that set of memories as well). Something similar was done with the Barry Allen Flash in the Flashpoint timeline (at least in the animated movie; I haven't read the comic version) - he retained both full sets of memories after he changed the timeline back.

Now that I think about it, an infinite multiverse would certainly explain the cartoon series with an intact DeLorean...

Sangraal can be read as San Graal or 'Holy Grail', but there is another interpretation - Sang Raal, or 'Blood Royal'. With the inventor named Scarlett, I suspect that there may be a much more nefarious origin for this miracle drug, one that might require human donors...