Realistically if Cain stays champ 3 solid wins in a row should put Mir back into contention, he's known by casual fans and he's good at selling fights. Now, whether he can string those kind of wins together again we will have to see.
As for Big Nog, he would also have to string some wins together but since he was already destroyed by Velasquez, I don't see a rematch happening. He also probably wouldn't fight Dos Santos. So really he needs Overeem to beat Big Foot and become HW champ... plus he has to beat Werdum and possibly Cormier if he beats Mir. There is a very slim chance that all works out in Big Nog's favor.
Right now I think there are more interesting matches for Mir at the top of the division than Big Nog, which would help him get to a title quicker. I'd like to see Mir against anyone near the top of the division other than Dos Santos again. Nog on the other hand, probably won't fight Velasquez again, wouldn't fight Junior and since Big Foot has the minotauro tattoo on his arm he probably wouldn't fight him neither that doesn't leave him a lot of routes to take to a title shot.