I say give them back after the Egyptian governmnet pays for the expedition and excavation costs (at todays dollar) associated with finding these items in the first place, Oh yeah be sure to throw in the cost for secure storage and maintenance these man years.
I might want to see the Rosetta Stone some day (it has historical significance). I suggest the consider the possibility that the items would not be returned.
Muslims cared NOTHING for preservation of ancient artifacts and cultural goods for 12+ centuries. They still largely despise them as un-Islamic (witness the Taliban destruction of the ancient Buddha statues with barely a peep of concern from the Muslim world). European (and later American) researchers began to discover, archive, and preserve countless such objects. Once ancient art and archaelogy became valuable in the eyes of much of the world, suddenly Europe and America are supposed to “return” all of the objects that were SAVED from being treated like trash for centuries (so many allowed to decay or be destroyed, etc.).