Of course it is is easy for me (and for the rest of the board) to say what we'd do under the circumstances you describe, but one certainly can't scuttle after that last person leaves the vessel unless one has artillery on the rescuing vessel.

The fear of running into something (a container or abandoned vessel or whatever), particularly at night, is a worry I try to keep in the back of my mind when at sea, but it is still there. As such, I've given some thought as what I'd like to think I'd do if I had to abandon my boat with no chance of it being salvaged. The plan is to close the sea cock for the galley sink, and make a significant cut in the sink's hose. The last thing to do before leaving the ship would be to open the sea cock a little bit, not a lot, so water would slowing enter the vessel. If it took days to sink, so be it. But in this way if the rescue were aborted, I could close the sea cock and still have a vessel that floats.

Who knows if in the heat of the moment I'd ever do this, but this is the conceptual plan. I don't believe I would not be thinking up a plan during a rescue.