Nvidia CEO Jensen Huang has resigned, and the stock dropped sharply premarket — bad news for Nvidia investors in the short term, but the company's underlying business may still be strong.

• Huang's exit wiped out a huge chunk of Nvidia's market value overnight, with the CFO temporarily stepping in.
• Carlos Ghosn, the former Nissan CEO who built and then lost control of his own company, says Huang will be very hard to replace because his years of experience and relationships can't be copied by a new hire, even someone equally talented.
• Ghosn, drawing on his own ouster from Nissan, says CEOs at this level face crushing pressure from shareholders, employees, and family, and that stepping away can be an understandable choice rather than a failure.
• He points out that after he left Nissan, the company cycled through three CEOs and lost most of its stock value, a warning sign for what weak succession planning can do to Nvidia.
• Despite the shakeup, Ghosn says Nvidia's products and market position remain strong, and he would hold the stock rather than sell or bet against it, while waiting to see who takes over.

Outlook: Nvidia's stock reaction looks like a short-term shock tied to Huang's exit, with the real test being whether the new leadership team can keep the company growing.