In our campaign the Lunar empire has lost the Provinces at least as far north as Tarsh. We had occasion recently to go down there (we are Lunars coming from the north). The assumption was that in Tarsh (Sartar had been lost years ago) all Lunar temples were gone (they hadn't converted them, as some Christians did with pagan temples but just razed them). So the main square in Furthest had places with just rubble. Things were tense and sullen. There had been killing, but then they couldn't kill everyone. Lunar resistance groups make thing even more tense.
For us, it wasn't as bad as it might have been, since the Lunars in the party only had to pose as "ex-Lunars", like a lot of the population, rather than try and pretend to be "Orlanthi". In Sartar, you probably would see people killed and temples razed (or converted). There probably would be much of a Lunar resistance though what happens to "collaborators" would be an issue. I think at best they would be bullied, raided, and treated shabbily. At worst many of them would be killed.