I've known about this since it happened in 1992. For those who don't know the story, Ozzy wanted Sabbath to open for him on what was gonna be Ozzy's last show
Sabbath had just finished up the Dehumanizer tour and depending on what story you hear Dio either refused to open for Ozzy or his contract with Sabbath ran out. Dio had only signed on to do one album and tour with Sabbath and these shows happened right after his contract had expired with them. Those are pretty much the reasons why they asked Halford to step in at the last minute. Weather the story or Dio's contract is true or not, it's really up to him weather or not he wanted to open for Ozzy. I think this had more to do with Ozzy/Dio having bad blood than anything. I've never known Dio to miss an opportunity to perform for the fans because of a contract running out. It's completely out of character for him.
I know sometimes stuff get past us but this happened awhile ago. You really need to get on top of things Fonzbear