We could offer two ways from that in fact. Either 500M or five-six months of activity. That would be better in fact for some people and would put end to that arguing. I believe the latter thing would be better to keep factions active...
And 500M, okay... But removal from the list after 3 months of COMPLETE inactivity. There are vacations or there could be hard work for some people, for your information. There can be moments when users weren't active much after 28 days and hit 3 hours only, but they could become active again in the next 28 days... So... What's the point? Month is too short for instaremoval.
Also, how does it apply for January and Febuary, the latter being the shortest month, but both being semestral examination period? Same with June and July.
It may also lead to absurd situations, because: X faction became less active and they need to obtain money, again. So X faction is again unactive, because all the money is earned on indie or Y faction character.