This is a case when both parties are at fault. If the driver of the car ran the stop sign, then he is responsible for failing to stop. The fact that your brother was riding his bike on the wrong side of the road puts him at fault as well. A bike is considered a vehicle just the same as a car. The bike must travel in the proper lanes, signal turns by using hand signals and obey all other traffic laws. Once he got on his bike and rode on a highway, he was no longer considered a pedestrian.
Hopefully your brother was not hurt seriously and bike repair is the only cost he will realize. Riding a bike to work can be very safe but the rules of the road must be adhered to by all. I believe both parties had some blame. If the driver fled the scene of the accident, that person definitely deserves a ticket. How the insurance company settles these matters when both have fault, is a mystery to me. If your brother does not have auto insurance, he may be able to have his home owner's or renter's insurance company plead in his behalf. If he is uninsured by any of these, contact your state's attorney generals office. They will provide assistance.