I was wondering when a player quits and his building goes into a state of decay then collapses his thralls remain for another week I believe but once that time limit is up do the thralls disappear from the world or do they die and drop whatever equipment they are holding?
I’ve never ever seen a thrall or pet decay so my best guess would be that it is checked at server restart 
Good question , as I never seen it ( I think you must be extremely lucky , first to be there at the right moment , and second to notice it ) i can’t answer the question , I have witness several base popping “naturaly” as I passed not far from them ( it’s like a surprise firework 
) and maybe ( if they just disapear) i have been near thralls disapearing but didn’t notice / pay attention to it .
I hope someone was more “lucky” and can answer this question I now ask myself also