I'm not so sure about the 2nd part of that. While still vulnerable to having some troops cut off, especially in the area to the south of, oh, say Amvrosiivka to Krasnodon, the Ukrainians have significantly pushed back the rebels, who themselves will be cut off in their entirety if Kiev can manage to close off the remaining 20 miles or so of border that Ukraine presently does not control...
There is some HEAVY weaponry fighting going on: I've seen comparisons of intensity to WW2, although in a more limited area of course. That is probably overstated a bit, but this is nothing like U.S. operations in Afghanistan, for example. Eastern Europeans and Russians don't mess around once they get going.
At any rate, especially if Russia pulls back on the air defenses for the rebels, and since Putin seems reluctant to commit to a major direct Russian ground op, I think it's possible that Ukraine can win this round before winter arrives. This creates an interesting scenario: Would Ukraine be content with the then status quo, or would they try to isolate Crimea and possibly start trouble from within, in 2015?
Now, if you mean that the US is unlikely to be directly involved in a shooting war with Russia, I agree. But a proxy war via Ukraine could go on for some time.
However, I think it's likely that he will use intelligence agents and propaganda to force another political change without the carnage in the Ukraine and do the same with the other former satellites., as Obama is far too weak in the knees to follow through with a US intervention in any way. Even military support seems to be off the table.
Allies, both former and current have already assessed Obama correctly for what he is and they realize that they cannot depend on support, even when it's promised by the US or it's agents. Our ability to project power has been decimated.
Putin will continue doing what he's doing, and nobody will intercede. Not unless there is a major change in US policy and I don't see it happening until the election in 2016.
In the interim he is going to have a unrestricted period of expansion. I don't see anything standing in his way but rhetoric, and even that is weak.