Warren Buffett built a fortune of nearly $60 billion from astute stock picking, but when the 83-year-old dies, the vast majority of the money he leaves his wife will be parked in a fund that simply moves in step with an index. The afterlife plans of the man nicknamed the Sage of Omaha, revealed in a letter to his investors earlier this year, underline a sea change afoot in the investment industry. Fed up with high fees and poor performance, investors are increasingly shunning active fund managers who promise to beat the stock market in favor of cheaper, passive funds, which simply track it.