when a fuel pump goes does sometimes the car will start or it will never start

I would say yes to both...because a fuel pump can be going bad. I experienced this with a truck. The fuel pump was in the process of going bad...sometimes the truck would backfire, quit, and not start. Then all of a sudden it would start. When the pump finally gave out on the interstate, the truck was done...it was not going anywhere until a new fuel pump was installed (lucky enough we were close enough to a town to walk in and get a new fuel pump).