I've personally witnessed a number of T12 and T8 ballast failures. The T8s were always the electronic. I've turned on fixtures and POOF- the fuse inside blew. Heard it. I've also seen a few that failed when I had them on. Have had a few Advance T8s and early generation Sylvania T8 ballasts that would smoke and get very hot when they failed.
As for T-12 Magnetic.. oh man do those things go! fire hazard. Those tar burners would get very hot and a few would flash arc when they failed, the others just got super hot and dripped tar out the ends and when I would go to change them, there was heat damage to the fixture from how how they got. And they smelled HORRIBLE.