Red herring tbh, Cobb's totem is a total red herring the whole way through as when they explain what it's for, they say "you can't touch it as it would defeat the point" totems go by feel. The totem is used to see if you're in someone elses dream, the idea being they wouldn't know what your totem feels like so you can tell if it's fake. A totem falling over can be faked, as can a totem endlessly spinning so it's useless in its function *unless* it has a very specific feel when he spins it. If that's the case, then whether it falls or not is irrelevent.
That said, he does hold the gun to his head until it falls, so it's possible that this was just a mistake by Nolan, something overlooked.
also that totem wasnt actually his, it was Mals. He just took it when she died