i think if an cmd like /leave will be added, then only the house should be reset, because if he wants to come back someday, then he havnt money anymore 
/leave already exists (DM, Race)
Also when you type the cmd then you should get a screen wich asks for a comfirmation 

like: 
Do you really want to quit? your house will be sold!  /no  /yesIndeed that would be cool...
But only if the person leaves
because I see alot of people own big houses and when they buy it, they are never online again  
