If Sophia fulfills all of Aiden's 12 tasks, there is no going back to normal (in the form: "We only do school lessons now."). Actually, this point is reached even earlier. Aiden will never rest. To do this, he would have to respect Sophia and this is already not apparent.
Someone like Morello would respect a contract made. If only because a breach of contract would damage his, Morello's, reputation in the long term. Aiden doesn't care at all about Sophia.
If Sophia resists Aiden, does all her duties, but never submits (no sex with Aiden), Aiden will never accept this defeat. Aiden would not accept even finishing the tasks at eye level. If Sophia submits, recognizes Aiden as her master, why should he give up his willing tool? He would go on and use Sophia to his advantage, even if he no longer fucks her himself.
There will be no joint "keep it up" at this school for both of them. Aiden and Sophia don't know yet, but one of them will leave this school. Sophia was always of the opinion that she could control the situation, but to get rid of Aiden, an external force / influence is necessary now and in the future. Sophia will never solve this problem on her own.
In that sense, Bennett's blackmail is a better choice. Bennett is a bastard, like Aiden, but he gave the impression of wanting to keep a contract.