Status Quo Ante

It is entirely possible that without obliterating the population of the Ukraine with nuclear, chemical, or biological weapons that Russia will never be able to fully conquer their neighbor; however, the Ukrainians are unlikely to be able to fully expel Russian forces from all their (now former) territory. This might lead to a constant state of war between the two, even if it is only limited fighting at what now might be established as new borders. Russian forces using conventional means may well never be able to subdue the Ukrainians, but the Ukrainians lack the strength on their own to push Russian forces back within their original boundaries.