The thing is that the current regime in Ukraine doesn't have much support hence why they cancelled elections. It's also worth noting that most people in Ukraine didn't really want to have a war with Russia. Zelensky originally ran on a platform of peace and implementing Minsk.

Guerrilla warfare requires support from general public who provide supplies for the partisans, hide them, and so on. I don't see that being the case in Ukraine. It's also worth noting that Russia managed to avoid this scenario in Chechnya already. In fact, Chechens are now fighting along side Russia in Ukraine. Looking at slides from this lecture that Mearsheimer gave back in 2015 is illustrative. First, here's the demographic breakdown of Ukraine:

here's how the election in 2004 went:

this is the 2010 election:

As we can clearly see from the voting patterns in both elections, the country is divided roughly across the current line of conflict. Furthermore, a survey conducted in 2015 further shows that there is a sharp division between people of eastern and western Ukraine on which economic bloc they would rather belong to:

What I expect will happen is that most people in eastern and central Ukraine will just accept being part of Russia going forward. Those who felt strongly against this either fled the country or died fighting because they were motivated to fight. Also worth noting that once it becomes clear that the war is lost there's going to be a huge backlash against the west, since lack of western support will be blamed for it by the hardliners. A lot of weapons that the west flooded into Ukraine disappeared. In fact, CBS did a study at one point that found that only just "30-40%" of the supplies coming across the border reached its final destination. There's no doubt that a lot of these weapons are now in the hands of various far right groups across Europe at this point. Ukrainian nationalist will undoubtedly link up with these groups, and once the war is over they will likely flee to Europe. It's entirely possible that Europe could start seeing the same kind of terrorism that we see in the Middle East after US flooded it with weapons and extremists.