What are the maritime laws for salvage of abandoned, but not completely destroyed, ships at sea?

What with all the cruise ships that have sunk in the past few years (Sea Diamond, Costa Concordia, Oceanis), I have an idea for a fictional story, but I want to know if maritime law will cooperate with the plot.

Here’s the plot in summary: Cruse ship starts to sink (for reasons yet to be determined). Captain and crew abandon ship, a.la. Oceanis, leaving passengers to die. Passengers all manage to launch the lifeboats on their own and leave the ship safely. One passenger stays behind and, heroically, saves the ship (how this will be accomplished, I haven’t determined yet), restarts the engines, and then sails home with his prize.

My question is: Can this passenger claim salvage rights to the ship under these conditions? Or does it actually have to sink before it can become designated a “ship wreck” subject to salvage?