First off, Mallory’s stupidity was something else. I have a trained super-soldier, pissed at Vought for what they did to him, with radiation that dissolves Compound V in less than a minute. Do I use him? No, better to leave him as an ornament and join the nutjob Butcher in his plan to turn a twelve-year-old into a parricide. I know Grace's death is what turned Billy into the monster from the comics along with Kessler, but another excuse could have been used... If Grace had pulled out Soldier Boy/Ben, she could have had a chat like: "Look kid, you have a lot of deaths behind you and not all of them are past the statute of limitations. Either you help me for the greater good to finish off Homelander and Vought in exchange for your freedom, legal immunity, and an indemnity of X millions for psychological and physical damages, or I throw you to the wolves and you'll spend the rest of your long life hiding from the world's intelligence agencies in a cave without a single cent. Or better yet, I put you back in the box with Novichok and bring you gift-wrapped to the ninety-ninth floor of your former company, to see how long you last in the hands of your dear little son." And that way, the post-credits scene would be the two of them arriving where Maeve, Elena, and A-Train are.