Never trust nationalists to be rational.
A Ukraine-Russia conflict would be a blessing for the US. It would force the EU to get closer to the US and put crippling sanctions towards Russia
So as the world moves towards Cold War 2, the US would have managed to deal such a big blow to Russia that it would take a decade for it to recover.
This would economically and diplomatically knockout Russia from the grand scheme of things and leave China "alone" without significant Russian help
As such, from US+puppets vs China + Russia it would become US+puppets vs China + very weakened Russia
That's a winning hand for the US. Minus points for distracting it from the Indo-Pacific and leaving a lot of space for China to make moves
All in all, even with some disadvantages I see this as a net positive for the US. As such, IMO war is coming between Ukraine and Russia
Russia will not invade unless Ukraine make a move. So far, what I can see from the Ukraine side is bluster. It is one thing to hold a knife to your own neck and scream like a mad woman. They would not really dare to actually commit suicide with no military aid from U.S. or EU. Even after the Russians invade and annihilate Ukraine militarily, they will not stay, they will pull back to the current border and leave a substantially weakened Ukraine to deal with the aftermath.
Russia was much weaker before and now is getting stronger. Selling gas with Nordstream II will add to their finances, but with energy prices much weaker before, they were at their most weakened state at that point. Even during that time, they fought and won in
Syria. Now their export will surge simply due to higher energy prices. Further sanctions such as kicking them out of the SWIFT system will have some very horrible repercussions for the U.S., Given that we just want to control Europe, going this far will do more harm to the U.S. Europe will set up an alternative system to bypass the SWIFT so they can do business with Russia. This will accelerate the decline of the U.S. dollar.
Of course the Ukraine conflict will benefit the U.S. and that is why it is happening. In the end, the world will still need energy from Russia, so their position will not substantially weaken. The Chinese are buying a lot of energy from them. I think the most difficult times are behind them. With the economy and other issues such a mess in the U.S. and EU, it is actually we who are on relative decline in the intermediate term. This decline will accelerate in the coming years. Putin just have to hold out for a decade and ensure a smooth transition to a government that will not sell out Russian interest after he departs, the geo-political situation will begin to flip in their favor. Given that he is just under 70, this is very doable.
In the current alliance between Russia and China, Russia contributes by being an independent military power that constrains the actions of the U.S. in Eurasia. We see this in Syria and Afghanistan. Their role in this will not substantially change going forward, Nordstream or no Nordstream. The economic competition and other heavy lifting are mainly done by China, so a small change in their economic status will not change the calculus in this alliance.