I am a Fellow of the International Association of Amateur Heralds - we only exist in cyberspace, like X Marks the Scot.com.

Every January, we have a census;
the secretary emails (not PMs) all active members;
members have 30 days to respond;
if there is no response the member is placed on the grey list (non-active)(forever);
at any time they can re-activate their membership with an email;
There is no loss of status.

I am sure a similar formula could be worked out for us.

Regards

Chas