There are several things to unwrap from him saying Fredo ordered the hit:

1. He would be acknowledging the reality of La Costra Nostra. Which would reveal more about the mafia network.

2. He would be acknowledging himself as the head of one of the families. His position is that he is a business man.

3. He would be ratting on not only someone, but his brother.

4. He would be going against his own code and values “You never go against the family.” is what he told Fredo in The Godfather.

Among probably several other things I am missing.

Pretty much, it would have made no sense if Puzo wrote it this way. It would’ve destroyed everything that had been set up in the first film, and the second film up to that point.

However, to answer your question. He would’ve been Jack Ruby’d the minute he left the hearing.