I dunno... this series is taking place on a fixed time-scale, so Ryon isn't going to age to the point where most people will accept him bein… moreg willing/capable of killing. That said, betraying his family, leading to someone's death? Very, very possible, even likely.
Gared may very well not make it - he's not actually part of the family, and his function seems to be exploring the Wall, and finding out what's up with the North Grove. Once those are accomplished, he won't contribute the main plot anymore, so probably either a) he'll die, b) he'll desert, c) he'll become involved long-term with whatever the North Grove is, maybe as some sort of caretaker, or d) he'll cease to be a playable character. I very much doubt d) would happen when a) could - heck, any of them happening when a) could.
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I think Mira has the red flag for the next killable playable character, depending on how you play her.
I'm thinking Gared will stick at the wall long enough for you to be capable of pledging allegiance to Stannis