While there are plenty of minutes for 3 elite big men, it isn't the minutes distribution that you have to contend with. The question for them will be, "Who is on the court when the game is on the line?" You can't answer with "whomever is playing better that day" and beat out 2 dozen other high-quality programs. Guys don't just want to win; they want to be the REASON they won. Otherwise, the best guys would all just play on the same team, every year.
Keep Tomi and Morez and find the "Next Tomi or Morez" to back them up. If Z leaves Cal, he's going to have every option you can imagine. While playing with his brother could be a draw, backing up his brother probably isn't going to cut it.