While I'm nowhere as severe as Terry, I do suffer from manic depression (bipolar II), and if it weren't for the support of friends and family I'm certain I would have offed myself years ago.
Terry suffered from an illness, but he was undoubtedly a smart guy. TempleOS and HolyC, even if they were niche, are certainly interesting projects, and aren't something that any lay-person could make.
While I'm relatively certain that his racist profanity-filled posts are how he's going to be remembered, I'll try and think of him as a misguided and misunderstood person who needed more help than society was really able to provide.