It is obvious Putin does not want to restore the former USSR; Latvia, Estonia and Lithuania etc have been part of the E.U. and NATO for a couple decades so that is a near impossibility. Though he does want to keep the number of former Soviet or Soviet aligned countries that have joined NATO at 14 and no more.
I'm not sure there isn't a disconnect there between the prohibitive reality of it and what Putin might desire.
Russia has put a lot of effort in recent years especially from around 2015/16 or so onwards in the Baltics and eastern Europe, making social and political inroads beyond the normal extending their influence large countries/entities do, actions which have lead to a worsening security situation in the Baltics including acquisitions of strategic locations in places like Finland and Gotland, some dubious events around Gotland such as large numbers of people linked to GRU visiting as "tourists", etc. and "leaked" plans for an invasion and setting up of S-400 installations on Gotland (
https://twitter.com/anders_aslund/status/1484907973013086211 I suspect in this case an overt threat through state media to try and make NATO step back*) so as to make it difficult for NATO to respond should Russia move on the Baltics, etc. etc. (granted most countries will develop a range of military plans as a contingency, even against allies, most of which will never be used).
If Ukraine had simply fallen with little more than a whimper from the West I suspect Russia would have pushed on with those plans using a variety of hybrid methods and more direct where they can until there was a push back - it is simply Putin's nature even if he didn't set out with a conquest of Europe (which I doubt he has any serious intentions as to) or a full on restoration of the empire. I think people vastly underestimate the security nightmare we'd have had to content with if Ukraine had rolled over and even now if Russia prevails even in this waker state there is still significant risk there.
I think it quite likely Russia would have progressed from Ukraine to using it to nibble away at eastern Europe using sort of carrot and stick methods, building up a large force on the borders of countries on the one hand, while using their political and social inroads on the other to try and flip countries to become somewhat like Belarus is to Russia, then hope to capitalise on the chaos that would produce in eastern Europe as a distraction from moves they might make in the Baltics although that becomes a sticking point where more direct methods would be required and the risks of escalation.
* Some comments in there about it being about the West fabricating fake news about Russian intentions, but I've seen more than one source of supposed Russian plans to that end.