No, it was the other way around, IIRC. Richard was allowed to *keep* Middleham, etc, as long as the Montagu male line survived. Once George Neville died in May 1483, *that's* when he lost his hereditary hold on the North. It's weird, but I've heard at least one suggestion that it was George's death that spurred on Richard's coup, not Edward's, because as King he could override the original contract drawn up by his brother, but he couldn't as Duke of Gloucester.
Maybe, but he would still need to become Regent and that was unlikely as English Kings had been crowned when they were younger than Edward V was now, and he needed to do that BEFORE George Neville died. If he was unable to secure power for himself before that, he could only go for the Crown
Pretty unlikely in my opinion. If George Neville die before Richard is able to buy off Latimer once the latter reached majority, then Richard will need to resign to keep Middleham for his life only and leave to his son only his remaining lands (if Edward of Middleham still die as OTL then the problem is solved as any future child of Richard by a second wife would have no reason for expecting to inherit Middleham and the Neville lands)
