They will have to go all the way to the Polish border, because Ukraine is not going to stop fighting until they have nowhere to retreat. Russia will be stuck with a Chechnya on steroids. I would also use a more modern election map.
The 2019 map. Blue is where Pro- Russian parties still were largest in 2019, in many places they used to be large they have collapsed, Russophone areas don't support the Pro- Russian position anymore like they did before (only in Ukrainian controlled Donbas are they still winning and in control of local politics).
Russia used to control half of Ukraine through the Pro- Russian parties. Now they don't and they haven't since 2014 when the Pro- Russian position collapsed in large parts of Ukraine where these parties used to be dominant.
Another map that explains this well:
Only part of the Russophone population of Ukraine identifies as ethnic Russian, many Russophone Ukrainians identifies as ethnic Ukrainian.