What do you mean by "their" territory? There is no question that Donbas belongs to Ukraine no matter how much Putin kicks, screams and supports separatists who are nothing more than terrorists.
Now, on to your other assertion, Russia is losing ground constantly. Their soldiers don't want to be there, they are poorly equipped and Russia is running low on pretty much everything their military needs. I think you are stuck on Russia supposedly being a super power. They have proven they are only a super power in regards to nuclear weapons and as poorly as their weapons have performed, I'm not too sure about that either.
They have a weak, antiquated and demoralized military. So long as we provide enough support, Russia will be forced out of Ukraine. I don't think that is debatable any longer. The interesting issue is what becomes of Crimea. I still think that will be the bargaining chip to end this mess.