Sadly there is nothing that can be done. If they implemented any type of debuff, the leavers would simply just sit at a node and go AFK. By the same token, I don't disagree with leaving WZ's, as sometimes you get peeps who completely ignore objectives, and make it miserable for those trying to win. The coin indeed has 2 sides. Either way, I don't see any change to the mechanics that would curb the issue, it's just one of those things.
I mainly agree with this. I would think a debuff would cause more harm than good.