Playing Romans against 3 bots and I have a question on the quarters phase of winter. Are the various Gallic factions under any obligation to vacate an area they have no control over
No. Quite the opposite: both the Arverni and the Belgae bots have explicit instructions to leave at least 1 Warband in each non-Devastated Region they currently occupy, even when they don't Control it.
The rules indicate "May" for devastated areas but is it the same for undevastated areas?
I can't find any Falling Sky rule or bot instruction saying that. Can you give exact references?
Related: when an area is "no control" does everyone vacate (aside from a Roman piece per ally/fort/paid "rent"?)
Only if it is Devastated.