With rare exception, I don't subscribe to the idea of "key men" in general, and especially not in this case. Even if I did, I don't think that Musk is acting in a way that makes him an asset.
I agree that Tesla, for instance, is doing good and important work. However, I think attributing Tesla's success, and net impact on the world to Musk alone is unsupported by evidence. That's because aside from initial investment/PR, and sufficient cult of personality to inspire people to work for him at the start, I don't see what Elon Musk is contributing to the company's work at this point. In fact, I see him as a liability and I think Tesla would be better off without him.
Candidly, I also believe that if Musk was less driven by his own ego, as he appears to be, he'd see that and step aside.
If Musk did not exist, and Tesla as a company did not exist, then all the engineers, expertise, effort, and capital that is currently with Tesla would be placed elsewhere.
Would all those people and resources do more good with all the other companies?