Gary Kubiak vowed that he’d learned lessons from a stroke that left him collapsed on the sideline in 2013, his final year as head coach of the Houston Texans. He told his family that he had his health under control, that they shouldn’t worry even as he took another head coaching job at the helm of the Denver Broncos two years later.



He recruited his son, Klint, who reluctantly joined him in Denver in 2016, afraid then that he’d be viewed simply as the coach’s son. He had another son, Klein, working as a Broncos scout. Now, Gary would get to see family more. He said he’d try not to pull all-nighters watching film anymore. That would ease his stress.



Five weeks into that season, the Broncos lost to the Falcons, their first defeat of the young season. Kubiak did his postgame press conference. The losing locker room cleared out. But back in the coach’s room, symptoms started to return for Kubiak. A stretcher arrived. Klint watched an...