as far as I know it's just 5 weeks.
If a user does not log in for 5 weeks in a row, his team goes bot.
once a team has gone bot, it can be replaced by a new user. This could take long, or this could be the first day, depending on the sign-ups for that country.
If a user can not log in for 5 weeks for some reason, he can contact the crew to prevent his team from becomming a bot. Note that you can not do this after the facts (you can not tell you where on a 6 week trip afterwards to get a team back) you must provide the info in front of the five week inactivity!!
They are not your friends; they dispise you. I am the only one you can count on. Trust me.