If the jetskis were relatively small (some still today are under 300kg - which is a lot... but who knows the size of the guy), I "suppose" you could just push it out... if you know the boat is going down you dont really care for scratching the entire bow or breaking the railings?
completely absurd? I dunno... Thankfully i've never been in that sort of situation, but if the captain truly feared for his life he'd find a way to get it off...
Any chance that whinch is manual? (i have no idea, its a honest question, no sarcasm)... I see a bulge but cant tell if it is just a motor or if it would be a handle for manualy winching it?