So how do you see this ending?
Because Russia know they are doomed either way. Please no

response such as Putin being assassinated or removed from power.
No “Russia” is not doomed either way. They “might” be defeated militarily but the nation and people of Russia won’t be doomed.
Their leadership might or might not be ousted.
Lot of talk about how that is not possible.
That too is an incorrect assumption. Few if any saw the collapse of the Berlin Wall or the collapse of the Soviet Union coming when it did.
Now will the Russian government as it is today be ousted? I don’t know and will not be surprised which ever way is goes. Yes I’m totally serious!
Will Putin escalate? Given the performance they’ve shown in Ukraine they cannot escalate against NATO in any protracted conventional manner.
They might continue to try and bluff with a conventional attack somewhere but they cannot wage major war conventionally.
Now because you and I have gone back and forth on this amiably I probably can guess your likely response.
Is the right of Ukraine to exist as a independent nation worth the risk of a nuclear exchange?
I say YES! Because if any nation is allowed to use threat of nuclear first strike to impose their will in today’s geopolitical reality. Especially when they were the initiator of conflict. It is a surrendering to the threat of nukes and that threat will be used again.
The response to a threat to use nuclear weapons when the aggressor nations conventional invasion didn’t go well should be viewed as a nuclear first strike threat and it must be countered with MAD.
That’s called the OBR doctrine