The only reason they occupied Crimea was because it looked like they were going to be kicked out of the base by the new government. So you are just letting them have land they had a lease and agreement to use for a few decades. Now if they move into the Ukraine proper, you have a good point. This is not Georgia where they had no lease or agreement to use land. What if Cuba was going to kick us out of our base ? Yes Obama would probably hand it to them on a silver platter, but we have been there for decades.
For Gitmo, I think we have a lease in which both parties have to agree to end it. I think we give them $2000/year for the lease. They, of course, always return the check.
The Russians see the Crimea as absolutely essential to their security, so they will be nearly impossible to remove from there. I think they could also encourage a separatist movement in the eastern and southern sections of Ukraine. This would create all sorts of problems, needless to say.