Anyone suggesting handing over Haochen ought to be suspected of colluding with the demons. After all, it's the first time in history mankind can do something about the demon god pillars, that is, permanently lower the demon's war potential. Even if the demon emperor promised to withdraw the troops after receiving, and killing, Haochen, it means absolutely nothing. After that nothing would prevent the demons from breaking the promise. Kind of like in RL a certain nation handed over its nuclear weapons in exchange for assurances of others respecting its sovereignty, yet years later that nation is now fighting for its very existence. Agreement papers are nothing but toilet papers if there're no consequences from breaching them.