It reaches a stalemate and the south east of Ukraine becomes separate state eventually annexed by russia, Ukraine joins EU and NATO
Ukraine withstands until europe and the US ramp up production and Russia collapses and fragments like the spanish empire before it.
Overall escalation continues in flashpoints around the world, nuclear war renders previous options irrelevant (congratulations if you live in the southern hemisphere, you might live to get an anwser correct!)
The US and europe abandon Ukraine over politics and disagreements, likely NATO and the EU collapse due to folding to military agression
Russia conquers Ukraine and then the rest of europe as they turn around in fear and cowardice, unwilling to fight
