Well, within the small area within artillery range of the former line of demarcation, which is considerable less than the eastern half of Ukraine.
After their defeat in the Russo-Japanese War the Russians re-built their armed forces and became considerably more aggressive. But that was with enormous loans from France to help Russia as a counterweight to Germany. I don't think anyone will be stepping up to do that with Russia today, although China might help a little. With sanctions Putin would have to re-Stalinize Russia's economy to rebuild on that scale, and I doubt he can do it. But since NATO has made it plain they will not get involved outside of a NATO member being attacked by Russia, it behooves smaller countries like Sweden and Finland to join now.
I don’t buy “half of Ukraine” at all. They may have lived more or less normal lives, but, people in Ukraine outside of the war zone were still KEENLY aware and concerned about “the war in the East”, and not any less so than people in almost all of Russia. Over the 8 years there have been plenty of deaths and injuries of relatives, friends, friends of friends, etc., on the Ukrainian side, and many men are ex-vets and such, plus other civilian connections...