I dont know the answer Ezio but this may help. If you recognise that Imperator has its origin in King of Kings, then Kok rules state that "Until the rebels are eliminated, the city produces no tribute." which to me implies that while some rebels may be killed, the remainder will stay in possession of the city until completely eliminated (probably because they are surrounded and have nowhere else to run). In other words, they dont give up after a defeat as raiders do but remain in control of the city until they are destroyed. What do you think?
I dont have the Imperator rules to hand, so if you have a pdf of them perhaps you could share them?
I agree with you about rebels inside a town (they remain in control of the city until they are destroyed). But what if the rebels are outside a city that did not join the rebels and they were defeated in combat by a relief force ?
I've not a pdf file for Imperator