He'd lose, but it would be interesting to see if Prescott still stands as the 'token' union candidate.
Brown would run on economic experience and on being a younger modernizing Smith. Blair would run a pretty ruthless campaign backed by the majority of the Shadow Cabinet and PLP. Blair from 1994 to 2001 was a campaigning beast and Brown would have struggled.
He'd still make Brown chancellor or Foreign Sec out of 'unity' but this would be the best for the party as it would mean that Brown wouldn't get free rein over policy, or expect his turn of the leadership. Most likely Blair sacks him either in 2001 or 2003