Linus truly is a once in a lifetime engineer

I think you give him a little more credit than he deserves. There are many people who have the capacity to do what Linus does. The main thing I would be concerned with is transfer of knowledge. However, I would imagine there are probably some hardcore Linux kernel devs out there who are extremely knowledgeable.

I'm just really hoping it doesn't go the way of the Protestant offshoot of Catholicism - every disagreement results in yet another split.

We already have many different versions of the Linux kernel. I don't see how it makes any difference whether Linus is around or not as far as that is concerned.