Him and Steve Perry have the same condition.
Journey with Steve Perry tour would be hard tickets to get unless you come up with BIG MOOLA.
No.
Dennis DeYoung isn't sick. He's just a pissed off bastard. Feuded with the other band members (Tommy Shaw in particular), took his toys and went home. To be fair, Shaw left first but then came back. He hated the type of songs DeYoung was contributing, the rock opera stuff and thought the band should play more traditional rock-type music. They reunited in the late 90s and did really well but the same issues surfaced. DeYoung tried to sabotage the new tour by claiming he had chronic fatigue and randomly refusing to perform. He wanted the tour postponed. They went on without him. He sued. The remainder of the band won. Shaw hates him and even though DeYoung has made noises about wanting to come back, he's ignored. The squabbling is why there are several Styx classics you won't hear when the current band plays. Babe. Mr. Roboto. Won't play.
Steve Perry had a medical condition that prevented him from singing for years. It was really never an ego thing. Yeah, he did a solo album while he was part of the band. And when his mom died and the band was in flux, they disbanded. They all got back together and then he broke his hip. They waited two years for him to get surgery and be ready to go but he wouldn't do it. Then he got a little butthurt when they wouldn't keep waiting for him to decide he was ready to get surgery and get back to work. And then there was some thing where he had a voice issue and wasn't able to sing for seven or eight years. In fact, I don't think he's performed on stage but two or three times since like 1989. No major feud, he's just not able and maybe doesn't care to.
Thankfully I saw both bands before the fractures.