Which edition of the rules contain that? I ask, because that's not stated in the Advanced Player's Tome. If you're referring to the "glory in single combat" clause under Chivalric Code, that's a pointer to the "Single Combat" feature -what you're calling Suicide Geas- that's listed under Combat. I don't enforce Single Combat as a Referee. The idea that a Knight has somehow dishonored their leige by not taking on a threat that's too lethal, is rife with possibilities for RPing and presents the possibility of an adventure hook. As Ref I'd always opt for the narrative approach rather than demoting them to a Fighter.
But if you're a player with a Referee that's by the book - yeah, I can see it being a problem.
Anyhow, as I stated before I don't personally have a connection with B/X, having only had the opportunity to play AD&D1e when B/X was still being published. I agree with others though, that NG not publishing an edition with content that's close to B/X, isn't a good idea. But I guess it comes down to how they'd organize and layout a consolidated book - if it's crystal clear what sections are B/X and which sections are adding AD&D1e features, I could see it working.