The only problem is if the entire losing team quits when they are obviously losing, then the winning team gets no favor points at all. So even hearing, "GG, you guys won" and then quitting is BAD.
So, no, I'm not ok with people leaving when it's an obvious loss, and I don't do it myself. I always stick it out to the end, because to do otherwise would be screwing over the winners.
However, I will tell the people whipping my butt to hurry the heck up. Some winners like to loiter around getting the best gear, etc etc. Destroy the citadel already!
There does not need to be rewards to losing, there just needs to be a concede option, which, I believe, is in the 1.1 patch.