By skyforbes A huge example of this: I just found out yesterday that Billy Idol was planned to star in Terminator 2: Judgement Day (1991) as the T-1000. However before the movie could start production, Idol got into a very bad car accident, and was heavily injured, hence why Idol didn't end up playing the role of T-1000. That was a weird choice at the time but looking at it now, it's crazy that Idol almost ended up getting the role in the first place since he's a singer and wasn't an actor in terms of film & television in the first place to begin with.
As of a result, Robert Patrick ended up replacing Idol to play the T-1000 and the rest is history.