Alerted how? On real UO if a house has rented vendors in it after the IDOC phase it goes into a "Demolition Pending" stage. Players then have 7 days to claim there items (the time it takes for a rental to not renew) or they drop with the house.
This feature is already live on Heritage.
I am not against changing the decay timers on Galleons but it will not as long as 6 months. The problem is players can place multiple ships.
OSI would sent me an email to alert me my subscription expired, which is what triggers the 90 day decay timer on house decay, so you are made aware the moment decay begins. I had 6 accounts at one time, and a lot of times that helped me to stay on top of it.
Personally I would like to see more vendor houses, active ones with quality content that is stocked, there arent enough. By the way I have an awesome house 18x18 east of skara brae in Felucca, its what Ive spent most of my money on and no one has ever seen it

LOL I may make it another vendor house in the future.
I guess I dont feel that concerned for non-active members, and if you cant refresh your houses every 6 months, you are pretty non-active.
I would like to see the Galleons get a reprieve on decay, they are pricey. losing mine really took the wind out of my sail (if I may) and honesty affected my participation rate on the shard for awhile til I got over it.