I assume there won't be an option for 'hostile' players to simply come in and raze our town while we're offline; that'd be majorly discouraging. I'm imagining something like a siege period, or there having to be some sort of arrangement between the town and attackers for a scheduled battle over it or something.
I hope that will be possible to manage settlements like an RTS, so hiring military npcs to defend our citites.
Anyway we need to wait the next spotlight that will explain the city building.