How old is your ds @Peanutgurgle ?
I have no experience with serious ED but some experience with food avoidance due to autism.
You say he is depressed, has anything happened recently? How do his summer holiday weeks look like, does he have any contact with anyone, any plans with friends or family?
Is there anything he is interested in and if yes, could you stat at the end. For example if he loves ocean related subjects (hypothetically) you could visit an aquarium (or similar low-pressure activity based on something he is very interested in) and if that peaks his interest it will relax him perhaps enough to get a favourite save food? Or get a small aquarium!
Alternatively if you don't want to venture out, could you buy an ice cream machine and make ice cream together, he can chose flavour and all that goes in?
If he has favourite characters, try and find foods with packaging that feature these characters (e.g Star Wars, Disney, etc.)
If you have a Ninja you could dehydrate fruit as an experiment and see if he is interested in that. Go and collect blackberries and make a cake or jam with it.
There can be a 100 and 1 reasons for him to avoid food out of the blue. Is he self conscious suddenly and doesn't want to be seen eating? Try and eat in the dark or with the TV on and no one else in the room.
These strategies may be fully unsuitable but in the past we have overcome autistic "stubbornness" (for lack of a better word) with some of these. Try and take the edge off, and reduce his fight or flight experience if applicable.