There is a rule for mafias, groups, clans and families properties, as far as I know.
It says any property that belongs to the mafia, group, clan or family will never be lost for inactivity, like Corleone's, Gvardia's and Stracci's HeadQuarters.
I mean, if Daniel Corleone goes inactive for above three months, the property will be re-set and someone will hold it untill the owner comes back.
At least one administrator, which I don't remember the name, told me that.