It is unfortunate but people come and go, and some you must kick for inactivity or just not following your rules. You try to catch them on from time to time but you are just never on at the same moments. If I am missing something please tell me, but wouldn't it be great if we can request for MODS to come out to remove the chests just to relieve the island of some space? We wouldn't even need whats in them. At least I don't.
If you are the owner of the island and the player has been inactive for a while you can get a mod to remove the lockette on the chest, or at least in my experience anyway.
But you don't think it would be possible that if MODS had the ability to just remove them for us that it would be ok? Mods can take down our spawners for us.. why not the chests that we don't want on the island?
hmm.. well 1… hoppers aren't even capable of being used on sky block. and 2… I'm pretty sure it is against the rules.