Yup you just played yourself
Logically she did save Sofia already. She's not interested in the prince romantically, after all. It's useless for her to be interested in a butler. As a marquis's daughter, her parents will arrange a marriage for her. The only thing Cyril needs to do is to remove himself from the picture. That will leave Sofia missing him, but so what? Missing a butler won't cause her to bully anyone specifically, so she will avoid her bad end.
It would be troublesome for Cyril to disappear without a word to anyone, so he should ask to meet the marquis himself and explain he's not suitable to serve under Sofia anymore and should be relieved from his duties. For the marquis, getting Sofia married to a scion of another noble house would be the priority, so he should understand immediately what's going on. He would likely pay Cyril enough for the dude to disappear far, far away. After all, aside from outrageously making Sofia fall in love with him, he has probably done better work than anyone else could have, so there shouldn't be any hard feelings.