The majority of Ukranians in the occupied areas don't want to be part of Ukraine since the coup of 2014 and consequent oppression of Russo-Ukrainians. The ones that do (a large minority inside east Ukraine) and haven't left already are likely to leave or integrate.

Insurgency happened in the Donbass oblasts and Crimea in favor of Russia, because there was a large majority not wanting to part of Ukraine anymore.

If Russia were to take Lviv, we'd likely see insurgency against Russia.