Wow, Byers would actually fit this pattern, and I have a feeling he's going to go in the final season. I really hope not, as it would preferable to have the core Party survive till the end. But out of all the boys, Will is the most at risk.
The only reason I see Becky reappearing is if El goes to see Terry again before the final battle, which does have a pretty good likelihood but I don’t see how Becky could die.