Well, I guess the question for me is, do you want their behavior to change? 'cause I'm of the strong opinion that if someone's doing something annoying/frustrating/whatever, and you want it to stop, you should do something about it. But if you don't really care, then you don't really care.

I dunno, if it were me, I would probably tell them. But I don't necessarily have a problem with a couple months of inactivity, so that's just me. It would depend on the circumstances.