It would have been a worse decision to give him a pass. He might have been old school, a rising star in the family and wouldn't have flipped, but the mistake he made was too big and too public to ever be allowed to slide.

The thing to remember is just how precarious things were for the leadership faction. They'd just opened a civil war in the family and there was no way that they could have let Sonny live. Too many questions would have been asked about their judgement and possibly their loyalty. I don't think he would have had a chance without all the faction fighting but with it he had even less.