Well, if it's something genetic, it won't go away. Say, when you're touching something. If you stop touching it, would you lose the ability to touch altogether? No. Same for magic. The power is in their genes, therefore it can't go away. Perhaps it would weaken by them not using it. Perhaps they would get tired real easy. But it woulden't go away. If Miguel was Crono, he could not only use magic, but use all his other, non-magical techs. The only tech he uses is Holy Dragon Sword, an attack Crono never has and could probably never get, being as he has little to no access to Dragonian technology. FATE, on the other hand, has loads of access to it. She would just give Miguel the power needed and pass into him the knowledge of using the tech.
Oh, and it did sound like you mean loving someone means you want to crush him to bits. I'm very happy to say, I have a gf and I very much love her. And I've never wanted to crush her to bits. FATE, on the other hand, is FORCED into loving the humans, because she's programmed to love them. But she's just so jealous of them being alive she wants to crush them to bits sometime.