What will we do if anything?

I was reading on Yahoo news that the U.S.A and Russia are having a back and forth. We told them that the U.N and the U.S wanted the borders back to normal and Russia said NO. They have also publicly stated that they think the U.S's humanitarian effort is BS and that they are "concerned". My question is the following: If Russia decides you know we are going to stay where we are. We are going to end the war but we are not giving them back the land. What would the U.N, U.S, Ukraine, etc do? Or would they get away with it?