This is really difficult and quite a grey area. Just to make a point, is gender dysphoria an acceptable neural diversity, but bipolar affective disorder is not?
The solution? He was a master communicator. He would tell me when he was having a manic streak and took on more work. When he was going back down, he communicated that and I took on more. If he started going unresponsive, I reached out and asked, and he told me where he was and what support he needed.
Now he's doing better and found the right medication, but crivens, I've been in a lot of other group projects, and I really miss him.