Don't worry, I am pretty sure that, if
Le Stag even plans it at all, that would be a decision similar to the condom or anal situation. Even on the sub path you can be the first that has analsex with her and the first to go raw, don't doing those two things still depended on the decision we made, hell, we could still have fun with Ashley even. Chastity would most likely be handled the same way.
On a side note tho, as you elude to: Chastity can be done without completly denying sex, as more of a "she has control" thing. A "gets off when with her, but when alone the MC can't just jerk off" kinda deal, as well as a point for possible humiliation stuff (be it teasing the mc for it, or making it known to ashley/nathan/ect so they can tease with it). So I really hope we get that possibility even if Le Stag doesn't want to introduce a possible "no sex" on the very sub route.