Don't let me interrupt your doomsday preps but here's what's going to happen before they ring in the new year:
1. The war will be over. The Russians made a mistake the first time thinking a show of force would be enough to bring Ukraine/NATO to the negotiating table. It didn't so now they will do it the hard way. The current mobilization will be complete before the ground freezes and then they they will move on the hard surface. What's left of the Ukrainian army at the end of it will be huge numbers of separated body parts.
2. No, nuclear weapons will not have been used.
Generals on both sides may be stupid but they aren't dumb. Conventional ballistic missiles will about it and there'll be plenty of those flying into Ukraine from Russia.
3. Zelensky will be dead, either from a drone strike or shot by his own generals. After which Ukraine will sue for peace and NATO will pretend it all went to plan (just like Iraq and Afghanistan).
4. Europe will suffer a hard winter. Europeans will burn firewood and old clothes to heat themselves. The resulting discontent will lead to more rightwing takeovers. Meloni is the first. Scholz in Germany will be gone.
But, hey, keep stocking up on tuna cans and bottled water.