From the Russian perspective, they seem to view NATO encroachment into Ukraine as an existential threat to their survival. IMO they will not cease hostilities until their objective of de-militarising and de-nazifying Ukraine are complete.
On the other hand, the West continues to escalate the situation and doesn't appear to care about Russian motives whatsoever.
I don't see this ending any time soon; neither side appears to care for the motives of the other and so far show no signs of backing down.
Will the West ultimately accept a Ukrainian defeat if that's what it comes to, or if that's what it takes to avert nuclear holocaust?
What do you think?
I don't think Ukraine geographically is as conducive to a partisan war as Afghanistan is, either. That said I don't think a full military victory is on the cards anymore, depending on how optimistic you are about Russian Armed Forces Ukraine either keeps sending armies and NATO equipment into the meat grinder until Russia runs out of artillery shells or they're just completely stalled out and won't make any more substantial progress.
I think you may have that a little backwards. Currently Russia is doing just fine, using a fraction of their full military potential as Ukraine burns through their own armies and supplies (which already happened for the most part a while ago) and then NATO stockpiles. Russia could keep this up for a very long time and be just fine. The big question is whether NATO (in other words, US interests) will seriously escalate the situation and bring us into WW3.