IIRC they need to fly the cold war jets like this - below radar - as their electronic capabilities are too bad, so a more modern russian jet could launch a missile at them just before the old Ukrainian jet sees a threat.

That is one of the reasons Ukraine urgently needs more modern material like enough numbers of F-16. While also being not the most modern jets those at least have some decent radar capabilities and can also be used as interceptors for air defense.

Of course Donbas will join Russia with your scheme. All the Ukrainians have been displaced. It is nothing else but colonization of Ukraine by Russia.

To be fair, only the people who lived in Donbas until the little green men invaded 8 years ago would need to be asked in a referendum.