I'm also reminded about the state of HP once the founders retired. My understanding is that John Young and Lewis Platt preserved the HP Way. However, Platt's successor, Carly Fiorina, moved the company far away from the HP Way, and HP hasn't been the same since.
This is a sad time for NVIDIA. I hope NVIDIA is blessed to get a Platt and not a Fiorina.
If someone else that wasn't directly trained by Jobs for years was hired, i'd argue that the culture would start to falter because one thing slides somewhere, then another, then another an soon enough 'A players' don't want to sacrifice their core years at a company that isn't instilling the values they want to work under. Cook himself almost went down that path with his budding career at Compaq. His family thought he was nuts to leave the growing company for Apple of all places. They didn't see the values that Cook saw in Jobs.
Apple was saved because it abandoned all its pre-1997 software and adopted NEXTSTEP, which Jobs created.