With the relationship & trust he's built with Trump...however much that is real, it's the best chance we have at ending the 70 year Korean war.
Whomever would take over, even his sister, Trump would probably have to start at square one again. Assuming that would even be possible.
The irony is that the world may need Kim to survive in order for he and Trump to be able to get the deal done during Trump's second term.
God knows what He is doing. We, on the other hand . . . .