I made a Huge QQ thread about this after housing was introduced, SE had said something about taking away FC houses from ppl who were inactive... Blah Blah Blah. I didn't find it fair to spend all that money at the time and to lose my house, if for some reason I was unable to play. 2.3 rolls around and I had some IRL stuff happen and I couldn't play. I own a small FC, people were quitting and there was just a few of us left. Well 6 months go by and things in my life are better and I was able to start playing again right before patch 2.5. Luckily my FC house was still there (thought it would have been gone) and my leadership passed to one of my alts and not one of the inactive players in my FC.

I get 6 months was a long time, I really did think the house would have been gone. But thankfully it wasn't. As I said back then, if SE needs to free up space for active FC's, They could remove the house, but issue the FC leader a Voucher or Land Deed for the same size land/house. You would lose all Furnishings, but at least you can get a house. But I would say after 90 days after inactivity, no less.