
The brothers whole deal was that he was obsessed with soongap, so him forgetting all about him is actually a blessing in disguise for both the two mcs and a curse for the brother. I wouldnt say he got off scotts free bc hes still not truly himself, hes probably forgotten a lot of things and that means hes not able to live a normal life (think about the guy bongchon almost killed to save his dad, that guy was not normal)
I think in the end him forgetting was the best for soongap bc he never wanted him dead but he also had left everything from his old life behind him, half brother too. This way he will never show his face again and soongap can heal
I know the author has a soft spot for pilgyeon I just cant prove it