Yes, of course. The implication here is that someone would stop running in order to enable a defection, but that's a fallacy. People can (and do) defect for reasons other than knowing when the game will end. The problem is not the defections per se (those happen all the time), it's the fact that if the end of your term is known then not only does that force you to defect (if you are rational), it also forces everyone else to defect if they are rational.