I think given the current deployment (and all other things being equal), Moscow could (could, not will) overrun the nation from the north and east in as little as three weeks.

If that turns out to be the case, it comes down to will and patience-- can/would western sanctions outlast the Russian occupation of the nation. I do not think the western nations would directly aid Kiev and I think Putin knows that and counts on it; keeping the conflict regional in scale.

Given the anemic reactions by the west to the Russo-Georgian war and the annexation of Crimea, my glass-half-empty bias gets even more so.