Russia is implying that if NATO aids their puppet state and Ukraine actually invades Russian held territories then Russia will escalate the war. Europe has been pretty lucky with the weather this year, so natural gas demand and thus the pressure Russia can exert is minimal which makes them a bit optimistic in what they can get away with. Russia however has been holding on to the areas it initially intended to capture so to Putin, the war has been successful and can be over at this point.
It’s all just saber rattling at this point, but air and ground offensives on Kyiv once spring comes and invasions into other states such as Czech Republic (which is like Ukraine, divided into ethnic groups that really don’t care about their central overlords), and it seems Putin has enough clout to pressure Belarus into the war, which would be devastating to Europe’s and NATO’s hold on the arctic areas.
Winter isn’t over yet though, if the warm front ended in Europe, the war would be over in no time, at this point, it’s probably going to be another year of fighting.
Russia is asking Ukraine and Biden into a peace treaty that sees the current occupied territories part of a separate state, probably allied with Russia, like Belarus or Kazakhstan. Biden will refuse, as will Ukraine, neither of them are willing or able to declare defeat. Are they bluffing? No, Russia’s army is bigger than all of Europe’s combined, everyone knows they have been staging new gear that’s significantly more powerful than what they started with last February. Right now Russia is playing chicken, hoping Zelensky gets his hopes up and starts attacking those staging grounds and that would be sufficient reason for Russia, China and co to flatten Ukraine.