Seriously, how can it go further?
He doesn’t have the economic or military might, or domestic support to push deep into Europe, let alone be able to hold vast swathes of land. It’s just not possible, there’ll be bluster and he’ll use other forms of ‘warfare’ but unless he’s become reckless with his own survival or there’s an aggressive move against him, he’ll not take this further than Ukraine, and maybe other countries that don’t have a robust defence.
Edit: I’m conveniently forgetting about nuclear and wmd warfare here.