A little more info, please? What meds is he on? Is it hard for him to eat, normally? Does he throw up randomly or after eating or some other time of day/night?
If he is on riluzole and does not seem to have anything else going on, since it can cause nausea, I would stop it. Was he depressed before these issues or is he depressed because he doesn't feel well?
If you can't keep him hydrated, he's not talking himself into giving up, and/or stopping riluzole doesn't help, I would certainly get a nurse practitioner out (most communities have some that do house calls) to assess him, or do a telemed visit to have him assessed for gastoenteritis (or see someone in person -- but you kind of made it sound like you guys are hunkering down).
I would certainly shop creatively (on line, of course) and see what he might like -- changing the temp + consistency of food, using a straw, oyster fork, smaller spoon, lots of things could help. Some PALS do better on sodas, some less; smoothies, soups, chicken fingers, tater tots...don't know what stage he's in, YMMV.
All you can do is make a move to break the cycle. It all becomes self-fulfilling and he deserves a chance to make calmer decisions with you.
Best,
Laurie