I'm not so sure about that. I feel it depends on whether Putin still has at least some marbles left. If he does? Yes, he realises that leaving a legacy of "war criminal who nuked Ukraine" isn't actually what he wants so the threat of nukes is making a point to NATO to stay out of it. If he's lost all his marbles, though, or if he's so far out of touch with reality as makes no difference? I could see him nuking Ukraine out of spite if it's clear he won't get what he wants, in a sort of "If I can't have you, no one can!" move. Assuming that there isn't a coup before that, or that him giving that order doesn't trigger a coup, etc, etc.