Also the Baltic sovereign nations remember very very very well what it was like under Russian oppression. They are not going back to that.
Finnish people remember burning their homes ahead of the advancing tank armies. We remember both wars and many of us have the memories in our blood.
Considering how superbly Russia is fucking up a simple ground invasion, I'd say any threat of nuclear escalation is empty at worst.
Putin says roll tanks into Ukraine? Yeah fine, military commanders oblige. They won't lose much over it. Putin says nuke the world? Well, about that... Even military commanders still want to survive.
Such a decision would be anything but de-escalation.
Either Russia is not a superpower or it's not that relevant.