I've been in a similar situation with social workers. Unlike the fine folks here who have commented on your post, I didn't know any better and thought I was responsible for my relative's care, when the social workers told me I was. This was incorrect. Do not do this!
So, right now, the social workers are indirectly guilting you by saying they're going to drop him off with no care. They're banking on you saying, "no, no, don't do that, I'll take care of him." Because who wants to think of their parent being alone with no care? Social workers pulled this on my mom once too, when my father was still alive (he had dementia and repeated strokes, among other problems, and was an abuser.) She said she wasn't able to bring him home and take care of him and they said, "OK, we'll drop him off at a homeless shelter then." She caved, and basically gave up her life to care for him. Do not do this!
The exact words that you want to use with the social worker is "unsafe discharge." They are not allowed to discharge him into a situation where he will not receive care, when he needs care, because it will not be safe for him. It sounds like they're trying to push their jobs onto you, which unfortunately is a thing that happens with some - not all! - social workers.
Does he by chance have, um, a strong personality or any issues with stubbornness? My relative did, and I strongly suspect that the social workers simply did not want to deal with them and decided to push them off on the next of kin (me) instead. As if I had any more hope of convincing them to accept their illness and follow doctors' orders simply because I was related!