Dealing with a car accident is never a planned occurrence; however, if the other party involved in the accident drives off from the scene it gets much more complicated and frustrating. 

Figuring out what to do if one entire half of the accident is no longer present can be confusing. According to State Farm Insurance, the best things to do are to stay put and gather evidence. 

Should I just let the other driver get away?

Yes. It may be very frustrating to watch the culprit drive away, but if you drive after them you will confuse any eyewitnesses to the accident. If an eyewitness sees two cars get into an accident and then subsequently chase each other off, it is unlikely that this testimony will help you very much. 

Rather, make sure to stop the car (move it out of the path of traffic if necessary) and call 911 if somebody has sustained an injury. Otherwise, call the police non-emergency number and make a report as you would if the other party to the accident were present. 

What sort of evidence should I gather?

If you own a smartphone or have a camera with you it is not a bad idea to take photographic evidence of any damage done to your vehicle or surrounding property. It is also a good idea to try and talk to any present eyewitnesses. 

Since many people do have smartphones these days, it is possible that somebody who witnessed the accident has video or photo evidence of the culprit. If somebody has a picture of the culprit or the license plate number, finding him or her will be very easy for the police.