It's possible. Devs keep saying Halo 5 will be the darkest Halo yet, and they still need MC for Halo 6.
Arbiter is fair game, though. I doubt they'll kill him though. They might kill Buck or someone from Blue Team
English
-
Blue team is fair game to an extent but arbiter commands the covenant and was a playable character in 2 and 3. They'd have a hard time off-ing him. Just hate they're making him help Locke.