That's why we're evacuating them further into the bubble, so that the population of that system is displaced, not lost.
There's a whole "post-Thargoid recovery" system state for systems we successfully defend from the Thargoids, and there are timers on the Thargoid controlled systems for attempts by us to re-take them. This means that human infrastructure can be re-built, and populations can migrate back to their home systems.
Dunno if it allows for a full revert, but the narrative mechanisms are in place for systems to be retaken, rebuilt, and repopulated. All while you get paid for being part of it.