Well the wizard loses his spells of he loses his spellbook or spell components, or at least that’s how it used to be.
Got nothing for the Artificer. It would be cool if they had tools or something like that they used. But I don’t think it’s about fairness as it is about immersion. Depending on the patron, especially the ones all about planning or intelligence, it breaks some people’s suspension of disbelief that they would make such dumb contracts that allowed the person to keep powers or gain new ones after betraying them.