The text does not mention secrets, I think it is more subtle than that. Buffett himself would probably tell you that there is no secret: his success is due to a combination of principles and judgement. The principles are those of value investing; provided these are followed judiciously, money will inevitably flow. Buffett has made no secret of the principles - he spends a lot of time trying to persuade other people to adopt them. Also he makes little secret of his own intelligence. The analogy is that of a new religion or faith (value investing, and/or Berkshire Hathaway) whose prophet (Buffett) must find a worthy successor (or successors) to keep the faith alive. The big question is whether he has succeeded in finding and training the right disciple(s) to do the job, and Munger is convinced that he has.

I am guessing the last sentence is your comment. Munger is implying that Buffet WILL pass (or has passed) on his secrets to a successor. Munger's rhetorical question is saying that someone like Buffett, who has such a long record of making excellent decisions over the course of his long life, is obviously going to foresee his death and thus ensure that the entire operation won't fall to pieces.

Buffett will pass ob the secret to his success?