The last time I saw him, on the "Happy Together" tour (an old friend was the bass player in the house band), he was in bad shape, so I'm not surprised. When he sang, you could distinctly hear a hissing noise, which turned out to be his oxygen tank. RIP
I grew up on Three Dog Night. Their greatest hits album was one of the records my parents had that I played over and over and over. He'll definitely be remembered.