It would have been solved and the US Navy called out, just like when JFK jr died in the plane crash. The Navy was called in to assist in the search for the bodies. NSNR
Mafia boss' daughter - the crime would be solved to his satisfaction allthough the Aruban authorities wouldn't know and would probably be investigating a few more "disappearances".
Kennedy daughter - would've probably given the boys whatever they wanted and then some, and hence no crime would've resulted.