Count me in as a devoted Joe Haskell fan!! I always liked him and wish they would have given him more interesting things to do.
As for what happened? Well, he didn't really go mad, since IMHO that was not the best of choices the writers could have made, although he did suffer severe anxiety given the things he had endured. After receiving treatment at Windcliff, he returned to Collinsport where he and Maggie got back together, married and lived happily ever after. So there!
Is this too optimistic an outlook for Dark Shadows? Maybe so, but I'm all for a bit of happiness for the characters.