I don't think this defense needs to replace anybody. Sendejo has his limitations, especially in coverage, but the other guys are too young and inexperienced for Zimmer to trust back there.
On offense, Brandon Fusco needs to improve -- so does Andre Smith at right tackle -- and yes, I could see a switch at split end should Treadwell get an opportunity.
Good for him. He could still help somebody.
Alexander did see more snaps than Sherels, overall. But yes, I do expect Alexander to be the next man up in the slot. Not sure why he wasn't on that play.