Firing Musk is never going to happen. It would collapse the share price, and investors know that. They can complain, but they can't fire him and not lose a fortune all around.
Apple did start spiraling after they fired Jobs. By the mid-'90s, Michael Dell famously said Apple should just shut down and give the shareholders their money back. What finally turned Apple around was Jobs coming back, and they wouldn't have even made it that far if Microsoft hadn't felt the need to put them on life support in order to stave off monopoly charges. So I'm not sure that's an example of it not being a crazy decision.
No, Apple stock became very diluted thanks to its near death experiences. Steve became a billionaire through Disney/Pixar as much as Apple, and Apple has mostly produced shareholder wealth for Vanguard 401k owners since then.
Depends who you ask. To be fair, it is not an apples to apples comparison (pun intended). Tesla is in a very different position than Apple in the early 90's.
With that in mind, the dialogue about Jobs / Musk feels oddly familiar with institutional investors having major issues and everyone else probably being too optimistic.