Yes, and Russia wouldn’t allow them to go back to Ukraine, either. The separatists were and are backed by Russia in the first place, and the population has changed radically since 2014. Before then, the split between Ukraniam and Russian people in the separatist controlled regions was similar with a small Ukrainian majority, but around half of the citizens have relocated due to the war so who knows what it’s like now. If there was an opportunity for a democratic referendum, it’s long gone.
I don’t think the England / Scotland example used by the original poster works here because Scotland is already part of the UK, it would be more like England trying to get independent Scotland to join England (or the UK) by backing an armed English separatist group, causing Scottish people to emigrate, and
then holding a referendum.
In this hypothetical England vs Independent Scotland scenario, England also annexes the Isle of Skye due to a large English population on the island and brings its army into Scotland to help calm the clashes between England backed armed separatist groups and local, legitimate resistance.
Sorry, too much wine tonight!
Just read that Putin has ordered troops into the separatist regions for “peacekeeping operations”