Hm. Straining his bond with Regret would be unnecessary. She offers her powers to those who request it (if she feels they are worthy), and would gladly take her claim and powers back if you just ask. And if you want her immortality without having to engage in her political messy business, you can renegotiate the terms of the contract. In other words, service to her is entirely voluntary. Prospective contractors are usually the ones trying to enslave her, not the other way around. Immortality from a pretty girl who's nice to you is too attractive an offer for many to pass up.