I dont really like this kind of plot, even if a character is totaly for sacrificing themselves, they wouldnt have done it because of : 1 sketchy guy might be lying 2 even if what sketchy guy says is true, he might not do what he promised and just kill you off 3 even if sketchy guy does do the thing, there is no way in hell he doesnt look for his own benefit and most likely screw what you value in process 4 he might no need or reason to destroy what you value after this but this guy is your enemy, he will most likely come for them directly after getting rid of you
so a "would you sacrifice yourself" situation never works in this kind of plot, because this is never about his willingless of the situation, because even if he does sacrifice, result will be only way too bad for everyone but his enemy