Well, I'm sure the writers know that they will lose fans if the story stops being about Syd. I mean, I completely agree that she is and always will be the heart and soul of this show, the family dynamic, her relationship with her dad and mom, you can't just take that away. I have faith in the writers and J.J. because I'm sure he knows his fan base... I mean, if you don't please the fans then the show won't be that sucessful. I just hope that they can somehow make it work. All of it.
Networks have a mind of their own. Personally, losing Syd would MAJORLY hurt the show in every way possible. Less fans, less ratings. Less ratings, less money which means less incentive for the show to be kept on air. (Or something like that) So if Syd did leave in Season 6, then the show wouldn't last that much longer. What I'm trying to say is knocking Syd off would kill the show and lose the fans, which means lower ratings. The networks surely know this, and they want more ratings. So it would be in everyones worst interest to knock SYd off. Or something like that.