If he had silently sneaked off the ship, would someone have noticed? How long would it take for anyone to notice that a ship without power and crewed by just 1 person was actually abandoned?
"It's enough, you might imagine, to make him think twice about going back to sea.
But he is determined. He says he is good at his job and wants nothing more than to pick up where he left off."
It is a sad state of affairs, whichever way you look at it.
There's something odd about this story because neither a passport nor money should have kept him there, unless there was literally some kind of watch for him, and/or the cash situation was really that extremely dire. That said, he was able to survive for 4 years so money had to be coming from somewhere.
I suggest that he was maybe being paid a tiny amount, and that he felt it'd be better to 'stick it out' as a nearly worthless cog, than to take a risky path home to what might be nothing anyhow.
EDIT: Apparently his passport may have been confiscated.