Just raided my first STR_ALIEN_BIG_BASE_ aka Colony aka former Embassy.
My two cents for the political debate: I think it could be fun if, after a country withdraws, some sort of resistance faction would emerge. But the Alien Embassy/Colony is keeping them busy. Destroy the Colony and while you wouldn't get the country back, you'd start to get care packages from the resistance or something. What that would be, I dunno. Radar boost within that country at least, helps finding proper bases there. Maybe money (obviously less than what the country gave while still on board). Equipment maybe but could be a nuisance if it's obsolete... Anyways, I think something fun could be done here.
And if you ever decide there should be a way to get a country back, supporting the resistance with some escalating missions would be the way to go. Or supporting with costly research/manufacturing projects that trades time and money towards getting the country back...