Currently, the only thing that happens if your FC is inactive for more than thirty days is if the FC owner/founder hasn't logged in for more than that length of time, then ownership will automatically be passed onto the next person on the member list, depending on their FC permissions, whether they were one of the earliest members, and also the last time of their login as well.

At this time, FC housing isn't affected, but SE have warned that in patch 2.3 houses that have been inactive for more than thirty days (in other words, not a single person has accessed the house in that time), then the land will automatically be repossessed by SE and your house disposed of, and the land put up for sale again. So as long as you have at least one person use the house semi regularly, you'll be fine.

This function currently isn't in the game yet though so you're safe for now. It's just something to be aware of for the future (patch 2.3 is due on July the 8th from what I understand).