Garret said he doesnt want me too because she looks like his mother, but Is there any reason I shouldn't blow magna' s ghost back out. What will happen if i decide to do so ?
Nothing much, really, like most things you do in the game. Garret just walks out of the room and is mildly traumatised but otherwise it is never mentioned ever again. The silver lining about playing a game where your decisions matter less than a Telltale MC's choices is that for the most part, there are near-zero consequences to doing just about anything in this game. The writers have made it pretty clear that it's their OCs' story, not yours.
You kick Liaden and Azzy into the pool of evil juice? Congrats, you have two bimbos and none of your party members feel disgusted by your actions.
Your corruption value is high? People still treat you as if you are pure and Cait is more than happy to bang you.
You bang the tavern owner's daughter enough times that the maxed out nursery you helped build is filled with only her pups? No worries, he won't ever make mention of it. So does his daughter that you banged. Treats it like a normal Tuesday.
You help Cait establish the equivalent of a branch for a high-class brothel in the equivalent of bumfuck nowhere
and you get to meet and fuck her god? Thank you, anon! Now the proxy war in Belharan can continue as usual and no, you still can't fuck me in the ass or knock me up. And you have pay an exorbitant amount to peruse the brothel that
you helped build. But there's a discount, teehee, so that's good!
So go ahead and do whatever it is that you desire in this game! No one will ever judge you for it. Not even your chad minotaur bro that you refused to help remove his cursed armor and turned into a woman. All because you wanted a cowgirl waifu.