Property rights and contract law make these scenarios a lot simpler.

So the question really is: Do we uphold such things when disaster strikes?

In a true survival situation, it can ultimately end up to be an every man for himself endeavor; in maritime tradition that is a distinct legal declaration.

I think it depends on the type/degree of disaster and, more importantly, if you are contractually obligated or legally responsible for people caught up in the disaster.

Obviously a disaster, let's say, involving an asteroid the size of Texas hurtling toward your place of business; I'd say you'd have little in the way of responsibilities to discharge...

In a more manageable disaster, like the lifeboat scenario you essentially have a triage type situation demands you focus on who you know you can save. You can't gamble and play what ifs, if you have a sure thing in hand.

The people in the boat (which should be full capacity) will most certainly survive, while those in the frigid water will not. Outweighing the juggler's risk of swapping people in and out of the icy water; you also have the added risk of desperate swimmers tipping over your lifeboat and endangering everyone on board.

Your responsibility is the contents of the lifeboat, risking further human lives is outside the scope of your charge.

You may have a gun and a position of authority but none of that gives you the right to order people out of the lifeboat that they boarded in good faith.

At this point the only possible outcome is to make a "new contract" with all the people aboard; this would most likely rely on volunteers to swap out with nearby swimmers. But this would still involve risks to everyone as mentioned above.

The clear action within your scope of now narrowly defined responsibility is to get the lifeboat as far from any swimmers as possible in order to avoid endangering those in the lifeboat.