Nobody is irreplaceable. And this includes Jensen Huang.

You can say (rightly) that he has vastly contributed to NVidia's success. Well, he's been well compensated for that to the tune of almost $200 billion. Will the company fall apart without him now? No. No, it won't.

Also, if they fire him today, nothing will really change for a few years anyway. The short-to-medium plans are already locked in.