Normal rules of Salvage apply
The owner can have them back, if they pay the total cost of the salvor in recovering them. wikipedia on Salvage law
In fact, it's probably more open than that - the items were deliberately abandoned to lighten the ship so that it would leave, so they might count as "Jetsam" under salvage law, and the lander is a "derelict".
I still reckon the Russians should have claimed salvage rights over the ISS when the Shuttle program was shut down. That would have been a good laugh, and an interesting point in international law.