Well, whether people stay or go, there seems no shortage of combatants on any given night. I admit to a bit of "RoR burn-out" myself - I think I've played a total of 4 games in the past two weeks (2 wins, 2 losses, if anyone's counting).
It says a great deal about a game that so many care so much about it, that they even feel their leaving a game should be such a cause for announcement. Well, the community will lose people, and will gain others. It happens - it's perfectly natural. Some will return w/ AoK, others will be lost to Asheron's Call, or who knows what. Hell, some real traitors might even get LIVES, never to be heard from again.
This is all part of the Grand Scheme of Things. Games come and go, as do Gamers. Perhaps in some desolate wilderness, there are still three guys huddled over a burned-out old stove playing "Rock, Paper, Scissors." Maybe even having fun doing it.
I will still play RoR, if not as much as before, and I will almost certainly get AoK, and can only hope it involves me just as thoroughly as AoE/RoR has done - like no other game before it (even Civ or HOMM II - blasphemy!!). I will still crush some of the same old foes, and still be crushed by other scum, er, folks. And that, too, is how it ever shall be.