If I drop some armour on the ground will it stay there forever until someone pick it up or it will disapear?
If no one picks it up, it will disappear eventually. Not sure if it is after hours or days. Back in time the items would remain, if nobody picked them up!
I think dropped items stay put until the server is restarted. Or sometimes even longer. There is a glitched blueprint in the east coast of Cape Corinth that's been bugging me for ages :D
There is also the other trick of placing one item on top of another. I don't know how it's done or how long it stays but once done none of the items can be picked up. Perhaps owner can but not sure about that either ...
Recently there was a carpet on the top of one building in Twen Peaks with something on it. I tryed to get it but couldn't. May be it was expesive carpet