He really wants an Emmy. Unfortunately, he didn't quite go far enough. If Stewie had been able to change the past later but chose not to do it, then Family Guy would have a better chance.
I think Seth is a genius think about it he kills off Brian has people talking about it for days and weeks and wonders what's going to happen now so more people watch it an then maybe somehow brian will come back
I think he incorporated the time machine breaking as a way to bring Brian back in case this back fired. Maybe he'll try it out a few episodes then, if the fans continue to be upset, have Stewie miraculously fix it then he go back to save Brian.