There are so many things wrong with this scenario. From the marijuana at the screen to hitting a pregnant woman with your car and then thinking it might be a good idea to leave! He was obviously high and trying to avoid a DUI/DWI, so hopefully he will be charged with one anyway.
Nobody should ever, and I do mean ever, leave the scene of an accident. The fact that the woman was pregnant with a baby just makes it all that much more wrong. I don't care who you are, it is wrong to leave the scene of an accident, period. He should be punished.
No one should ever leave the scene of an accident, regardless of who they hit. It is illegal to leave the scene of an accident. I believe you should offer help to anyone you may have injured in an accident, even if you may be in legal trouble for the accident. Even if it is an accident, someone is responsible. You should always wait for the police after an accident.
In any accident, the driver should take responsibility for his actions and should remain at the scene of the accident until the police arrive. In this situation more than any it is important that Jon Jones remains at the scene to ensure that no harm has been done to the other party and provide assistance if needed. If nothing else , he could call for an ambulance or make sure someone else calls for help of he doesn't have a cell phone.