Ideally, use a betting prediction market. But since this is probably not what you meant here are my guesses:
The odds of Russian intervening militarily = 40%.
The odds of the Russians losing the conventional battle (perhaps because of NATO intervention) conditional on them entering = 30%.
The odds of the Russians resorting to nuclear weapons conditional on them losing the conventional battle = 20%.
Ah, I see, given these estimates, I can understand why this does not look like a Pascal's wager to you. It seems to me that the odds look so grave to you because you gloss over several steps during this potential escalation. For example, "Russians intervening militarily" could be anything from posturing to weapon shipments to a surgical strike to a Czechoslovakia-style tank-roll or Afghanistan invasion. My guess that the odds of the latter is below 5%, as it has not happened since (Chechnya was the closest case and that was a Russian territory ac...
A Dan Carlin Podcast about how the United States is foolishly antagonizing the Russians over Ukraine. Carlin makes an analogy as to how the United States would feel if Russia helped overthrow the government of Mexico to install an anti-American government under conditions that might result in a Mexican civil war. Because of the Russian nuclear arsenal, even a tiny chance of a war between the United States and Russia has a huge negative expected value.