Well, if at all he's being realistic, if he wants to avoid cliches at all costs, he should continue to kill characters up until the very end, and not only at the relative beginning.
Take sports, in real life there are favorite teams losing the final or even the semi final. No one would make a sport movie about a team that loses a final or even the semi-final, but if the "game of thrones" is a tournament, there must be someone that stumbles at the last step.
Maybe Daenerys herself, imagine if she conquers almost all Westeros, and then makes a stupid mistake with King Landing in sight and gets killed because of it. Once again I use sports as a comparison, the equivalent of a favorite football team that loses the final because the so far excellent goalkeeper totally misses a catch in a very slapstick way. It would be interesting at least from a "realistic narrative" standpoint see something like this happen.