The way I understood it was that if the vendor is owned by the home owner, there is no renewal to the contract. Which subsequently means that you have to wait for it to run out of money before it will drop to the sign and start the 'final' decay timer.
There is a home on my shard, with one vendor in it, that has been in OSI status for well over 3 years that I'm aware of. Who knows how long it was that way before I ever noticed it??
They should implement something that either drops the vendor immediately once a house goes OSI, or raise the daily vendor fees to some outrageous amount so that the thing will go away within a reasonable amount of time. Once a house is in that status, there is no way for the home owner to get it back...which I know from personal experience and many hours on the phone with C.S., as well as multiple emails to and from a friend that used to be on the dev team.
Ugh.. That house I lost almost had me quitting the game permanently. Darn housing bug..