yes, he passed away. he got a bacterial infection.
the severums at the LFS where I used to work would do the same thing all the time. you bring the fish in, they are fine, then a few days later they clamp up, their head starts getting huge holes (like hemaxmita (hole in the head) but it happens in just a few days) and they are gone. it happens so fast you can't combat it.
mine did the same thing...