Did it happen to you?
did you ever injured after the game begin?
FIBA rules says that if the official injured and can not continue to perform his duties the game shall be resumed and the other official will officiate ALONE until the end of the game.(unless there is possibility of replacing the injured ref' by a qualified substitute official).
what is the rule in the NCAA/NBA?

NBA and NCAA are usually officiated by crews of three officials. If one goes down, they (generally) continue with two.

Playoff/tournament games, and the like, will generally have an alternate official available at the table to take the injured official's place in a case like this.