The so-called trouble is really Olaya's headache to deal with. After all, the Holy Sword has been extracted, the seal released, and then you go back and tell everyone the Demon King ran away early—isn't that setting someone up for failure?
But if you say the Demon King was sealed, then the moment he shows up, your bluff is immediately called.
However, that's Olaya's problem to consider; Duanmu Huai doesn't care about that.
But speaking of which, he's quite familiar with this Hero's shrewd move.
Selling out your descendants for power—well, a certain Emperor has pulled a similar shrewd move.
And he even tried to dodge the debt afterwards, but it turns out the creditor wasn't so easy to mess with.