The town and everything in it will be permanent - places, businesses etc. However, not everyone of the inhabitants will be there all the time, that's what I meant... So, the butcher may spend three months working in the town, then go back to "modern civilisation" and be a car mechanic or whatever until he comes back to the town. In the meantime, there will be another butcher in his place.
Ideally, these will all be independent businesses so it will be in everyone's interest to keep things going - they will be doing it for themselves, not for an abstract idea or "for the town". Initially, we'll have to organise and micro-manage ourselves, I guess.
The exception will be town magistrates (consul = modern "mayor") - these will obviously have to stay in town while their term lasts (one year, in the traditional Roman style) or at least while they "have the power". They had a very sensible arrangement in Rome - there were always two consuls, and they would alternate "having all the power" for a month at a time. In our case, this would allow the second consul to go back to Brisbane, Sydney or whatever and take care of his business there and then come back to rule the town for another month.