There is no need for OP's brother to sell his bike. The post says that the other rider was driving recklessly which was the cause of the accident. All methods of transportation have risks associated with them just some more than others. Would you tell someone to sell their car if someone they knew was killed in an accident? Probably not. OP should be there for his brother but any request like that will probably be meet with hostility and will help no one.

I hate to be cliche but unless you ride you probably don't understand the connection someone can feel with their bike.

OP: I am truly sorry for your brothers loss. Be with him as much as you can and listen. But understand this, your brother will probably keep his bike and keep riding. There is a whole subculture in the motorcycle world and there is no better way to remember a fallen rider than a memorial ride.