We do a annual spring cleaning of dead members as we have several members who's real lives mean they are away from the game for months of a time. When we do a clear out one of the questions we ask ourselves is based upon the current active membership will dropping down a tier level make it harder for the lower levels to be able to do the guild quests. You have to remember with a guild which can have and has had 100 members in the past due to the mechanics you have to lose 45 members before dropping down a size tier. The 2013 and 2014 clean outs did not drop us down, the 2015 clear out did drop us down but we only needed 3 new members to move us back up.
One factor I have not mentioned is the event's. During events we make GQ's optional with no time limit so as to allow members to concentrate on gaining event items. We use the Easter event for a activity check, with the spring clean following after event end.