As noted, very few - if any - of the talent knew that Roman Reigns was battling leukemia again before he made his announcement on RAW this past Monday night. The leukemia had been in remission since late 2008. Dave Meltzer noted in the latest edition of The Wrestling Observer Newsletter that few people in the company knew that he had ever battled the disease.
According to The Observer, Seth Rollins and Dean Ambrose were not even told about Reigns' diagnosis. An hour before the show a few people, including Rollins and Ambrose, were told that Reigns would vacate the WWE Universal Championship to open up the show, but weren't told why and that it would be explained his his promo. Reigns reportedly told Rollins and Ambrose to be ready to meet him after his promo was done, but they weren't told what the promo would be about. Michael Cole also knew that Reigns would be vacating the title to open the show, but it's believed he didn't know why. It's not known if he told Corey Graves and Renee Young beforehand as well.
Meltzer reported that Reigns was in a bus all day before the show, which he had requested. Vince McMahon wasn't at RAW, but was working throughout the day to prepare people who had to know about Reigns' announcement without providing specifics. McMahon reportedly first found out about Reigns' diagnosis before the weekend, on Thursday night, October 18th. Reigns missed last weekend's live events, but there was never a reason given why.
Triple H ran Monday's RAW and produced the announcers, although Vince was in constant contact with him. In addition to Triple H, it's believed that Kevin Dunn, Mark Carrano in talent relations and writers Dave Kapoor and Ed Koskey knew what the promo would be about. Stephanie McMahon and Michael Hayes were not at the show either.
The creative team was told that Reigns was vacating the title and there would be changes to the show. As noted, Dean Ambrose turning heel was always the plan, however it was changed to happen on Monday's show because they felt it would be more effective there instead of continuing with the originally planned storyline.