The problem, and a point I think most commentors here are missing, is that unless something drastic happens like a putsch against Putin internally, I don't see Russia ever backing down from this - there's too much national dignity on the line.
What I fear is that if their troops are pushed back, Putin will begin some kind of chemical warfare campaign and indiscriminately just gas the entire country's populace into oblivion. I mean, he's already being called a war criminal and has lost favour domestically- he doesn't really have anything to lose at this point.
So this is my line of reasoning for beginning negotiations. I don't believe we should be cornering a mad man and presenting him with no way out - there's no telling what he might do.
A diplomatic route should at the very least start to be considered where both sides compromise and both sides make concessions.
The alternatives look much, much worse.