In an interview, Warren Buffet suggested that if someone was perfect at the Final Four, he'd offer to buy them out for the EV (or even half the EV). If you aren't already rich, you'd be an idiot to not take his offer. It pays for Warren Buffet to buy someone out for their EV, because that minimizes HIS risk.

Even if the person refused the offer, Warren Buffet could go to Vegas and bet on the last couple of games, as a hedge.

Even if you're perfect at the sweet 16 (which has never happened), with 15 games left (assuming each is a coinflip), your EV is 1/2^15 ~ 1 in 32000, so your bracket is only worth $300M/32000 ~ $9k.