I do not agree with your definition of insanity here.The mechanics are how you interface with the game world. To not take the mechanics into account is to play a mad character who doesn't live in their world. Yes I consider not playing a literally insane character unless the insanity is part of their character to be important.
Mechanically, you yourself are less inclined to suffer a heart attack by exercising and eating healthier. Do you do so? Every day? If not, then I guess you should be considered insane for voluntarily not doing something that will keep you alive. Or what about taking additional driving courses to be stronger behind the wheel of a car and less likely to die in a crash from poor driving. If you aren't making that obvious choice for longer life, then I guess you just must be mad, right?
And this is why I don't agree with your definition.
We all make choices based not on one specific end result, but for any hundreds of different reasons. And choosing to do something counter to that one result does not make one "mad" or "insane". So someone who decides Necromancy is their magical interest and wants to focus on that... but then chooses not to because there's a chance they might have a shorter lifespan... is not more sane than someone else. Especially considering if living longer was truly that important, they wouldn't even be going out to adventure in the first place.