You realize that the Metropolitan Museum of Art built a new wing into Central Park around 1985 to house a ton of artifacts on loan from the Government of Egypt? If they demand them back, and the Museum has no legal reason to refuse, they will be left with an empty wing and the antiquities will ride into oblivion.
The empty wing should be called the “Cenotaph of Egyptian Civilization.”
I'd imagine politics to play a part, both Egyptian and American. Here, the MuslimBro'hood in power, will push the gears to empty the museum and send back artifacts for it's destruction. Egyptians like Americans, do not think with one mind. Egyptian curators across Egypt will make known their preferences for Americans to hold onto anything Egyptian until such time, even if never, the MB tornado blows thru their country; while Egyptian "leaders" lobby along with American "leaders" otherwise.