From what I understand of bus driving (my FIL is one), he could have called the police on his radio and had them track down the kid for assault. Probably too much hassle for this incident, but bus drivers are on the front line sometimes, and they’re not without resources out there.
I just hope the driver has a good memory for faces, and those kids try to take his bus again.
I believe featherlou is right… In L.A. I remember seeing a bus stopped, a woman (I believe) arrested, and cops questioning the others on the bus for just such an incident.