It was never really stated that there were any, to my recollection. If there were, they were likely to be military commanders and may as well be assumed dead at this point. Bear in mind, the province is a backwater as far as the Empire is concerned.
Was it? My understanding of the whole situation is that Gaius wanted to minimise casualties in the process of taking it over, not that he had any concerns that it'd put up too great a fight. After conquering the entirety of Ilsebard, the idea that Ala Mhigo would fend off the Empire is rather fanciful, to put it mildly. And "unity" would still leave the nation under the rule of its mad king.
Doma does indeed seem to have been pretty bad in some respects. Both it and Ala Mhigo were unruly provinces.
And, lest we forget, they sought to inflict a pretty similar fate on Gridania, as the Empire had inflicted upon them - but ultimately they were unable to do so as they were repelled by the other city states. Yes, yes, it was a while ago (80 years), but their warlike nature means they're not particularly different to the Garleans who came to rule them. So I don't understand why they think they're owed some great sympathy, particularly as the other city-states bent over backwards to accommodate them, often to their own detriment, or why I'm supposed to see the Garleans as uniquely mendacious.
That said, none of the city-states strikes me as particularly able to do much against the Empire (or even the Primals/Eikons) without the WoL (their deus ex machina) or, to a lesser extent, the Scions. The only city-state the Empire actively avoids is Sharlayan, and that is because it has formidable magic prowess and defences. I think recent spoilers in the story might also explain imperial reticence to move to that area, given that it's where the Scions originate in essence, and certain somebodies might already have their fingers in that pie. However, we'll see where its story goes.
The way it strikes me right now, is that it's a bunch of pretty zones whose denizens I'm not overly fond of. The music's good, though, especially in the Lochs.