Last I heard, BRK.A trades at a pretty hefty premium above the market value of its assets (not something you normally want to see in a holding company), and nobody knows whether a protégé of Buffet will be able to come anywhere near his celebrated performance.
Buffet himself does not believe that will happen. If you read the 2010 letter to shareholders, he states that going forward he does not expect growth in the order they have in the past.
That he and Charlies biggest challenge is to maintain a solid baseline of market matching, and occasionally beating, performance. They can't really go for the big wins any more - due to their market cap, a big win would have to be astronomical to give them growth like they had in the 80s.
