My chain of reasoning:

• if Ukraine loses (or has to enter a very unfavourable agreement), it's not due to Ukraine wanting to lose, but no longer having the means to oppose (after all, Russia is a bigger country and also inherited nearly all the weapons of the USSR, and that was a lot)
• thus, if Ukraine loses, inability or unwillingness of allies to support them is involved
• if subsequently, a victorious Russia recovers economically, Russia may undertake further conquests
• the next conquest could be westward of Ukraine, and a member of NATO --> path A to a really bad war
• however, Russia might be too exhausted to undertake another conquest soon, or might collapse economically, even into revolutionary conditions --> path to uncertain times
• however, there's another conflict waiting to happen: China is systematically training its military for attacking Taiwan, and systematically threatening Taiwan with military maneuvers and political statemements
• it should be noted that China has also had border conflicts with India and Vietnam, and territorial disputes with many more countries, though no claims against their sovereignity
• if Ukraine loses, this implies that Western countries will abandon an ally if pressed hard enough
• subsequently China will consider whether it can press Taiwan hard enough, and I think it will conclude "yes" due to proximity --> path B to a really bad war
• this development might come to a stop though, if Taiwan should surprisingly announce on some year that it has nuclear weapons and conduct a test

Conclusion: I have doubts, but yes, there is a potential for a chain reaction if it's demonstrated that international law does not have enough backers (does not apply if you are big enough).

Remember Trump is going to stop it before he is president! He is going to call Putin and tell him he better knock it off.

I feel like the Ukraine has one enemy. It’s just that the enemy has their hands in so many other country’s pots that those countries are either happy to help them, or obliged. But either way, I agree that Ukraine is unfortunately screwed.

World War happens when at least two great powers are on either side, according to League of Nations

Shame it couldn't've started with a better US government

That's a bold claim, not that I necessarily disagree with it. Are there groups of well respected historians that would agree that it has begun? I could only find a few here and there that think it has started.