Good question. Lots of things to consider.

At the time he was shot, Joe Colombo was free on bail pending appeal after being sentenced to 2.5 years for perjury, he was under federal indictment for tax evasion, contempt of court and interstate gambling (thanks to Scarpa I believe). So he was potentially facing serious, or at least a decent amount of prison time.

Persico gets out of prison in 1979, does he make a move to become boss in Colombo's absence? Does he make a move to become boss even if Colombo beats all the charges?

Even if things remain stable, Colombo would most likely get caught up in the Commission case and receive 100 years. It's a possibility that a guy with his ego could want to remain the official power and have his son run things, just like Persico did, and this could create a civil war situation just like what happened in real life.

Fun fact: Before going to work for Cantalupo Realty, Colombo was employed for six years as salesman for Pride Wholesale Meat Company, which was controlled by Peter Castellano and Paul Gambino, brother of Carlo Gambino.
http://www.nytimes.com/1971/05/03/archiv...d-of-a-new.html