I created a savegame between when DeSinge meets his grisly end, and when Guybrush throws the sponge into the machine. I did this so I could enjoy that final cutscene as often as I wanted without a lot of gameplay leading up to it. :)
Anyway, I loaded the savegame and realized I hadn't tried talking to Elaine when it was just the two of us. Guybrush says something about how they'll be all good once he tosses the sponge in, and Elaine says something along the lines of "Well, why don't you then?" When the master POV returned, DeSinge had miraculously reappeared, arms stretched out to the side! The sponge had also appeared on the ground -- and also in DeSinge's turban. You could even initiate dialogue with him, which seemed to reset him in "messing around with the device" mode. I reloaded the game at that point, so I can't say what might have happened if I'd continued (I wish I'd kept playing to find out) ... but clearly, DeSinge was not supposed to be resurrected at this point. :)
Also, is there any way the game engine will let you get to the main menu while the Credits are running? Once they start, you can't get to the main menu or quit the game without sitting through the entire thing or crashing the game manually. I understand if that's a deliberate move to encourage people to watch them through ... but I did that once, and it'd be nice to be able to watch the final movie without having to sit through the credits every time.