that's a good question. I would think it can so long as your stuff is there. If the game deletes it for any reason then no.

yeah but once you are kicked out of the event if you are the only one there it will close no or someone as to be there too for it to work?

I'm not really sure. As far as I'm aware the boss cave/arena's are open and existing on the map at all times, they are simply hidden in places you are unable to get to normally. As long as this is correct the stone should work. If they switched to an actual instance (map unloads etc...) then the stone would never work. And even in the prior setup if the area is wiped clean after all players are gone then there would be nothing to recover.