It depends.
If I was walking through the woods and stumbled across the wreck, I'd be inclined to at least attempt to return it, although the legitimate owner at that point may actually be an insurance company, not the family.
If I bought or otherwise owned the salvage rights--as is implied by the fact that you said an "expedition," a deliberate action--whatever I find is mine, subject to the terms of whatever contract I have with the previous owner. I might still try to find the family of the individual, but I would consider that to be my choice, not any particular moral duty: the duty ends when I acquire the rights to the wreck.
Short answer: details matter.