What becomes of most childhood bullies?

Hard to tell. It depends on the bully. Generally speaking, some grow out of bullying as an unfortunate phase. Others continue bullying into their adult life. Believe it or not, most bullies are not sociopaths. They are incredibly insecure and fragile people who turn to violence to buttress shaky self esteem, by taking out their rage and frustration on safer targets.
Sociopaths, dejected. And unstable individuals, or they learn their life lessons and grow up to be scent people. Some even run for president!