I LOOOOVE ERIC, I wonder how the timeline would be affected because of his existence
First, Nath probably dies a bit sooner because my girl made 2 sentibabies, however I don't think Emilie would go rogue with the Butterfly Miraculous... Like, yes, she loves Emilie with all her heart but she's also smarter than Gabriel (and she also has him to help her deal with her grief).
So... what if... instead... Emilie starts searching for the Guardian! Like, yes, Gabriel did search for a cure for Emilie for years and never found anything, BUT Nathalie did keep everything to herself 'til death, and also Emilie is smarter than Gabriel...
Maybe she uses the Butterfly Miraculous to get his attention (Stoneheart incident) BUT backs down the moment she manages to establish contact with Fu. So Emilie talks with Fu, and tells him that she'll give him the Miraculouses back IF they work together so they can find a cure for Nathalie.
Also, probably Emilie tells Adrien and Eric about the Miraculouses & the senti stuff? Maybe it was one of the conditions Fu and her agreed on 'cause those poor boys DESERVE to know.
Anyways, after learning the truth, the boys WILL help Emilie and Fu to find the cure, they won't take a no for an answer, they wanna help bring her mom back by any method possible. And... so they can help properly, they are given their Miraculouses! That way, Butterfly!Emilie, Chat Noir, and Shepherd Boy go find anything remaining from the old guardians (and they don't have to pay for expensive trips thanks to the Horse Miraculous).
And honestly, so many things could happen. Maybe they find Feast and manage to restore the order like in canon, which leads to Nath being cured! Or they can't... which leads to a villain Emilie! (Maybe Adrien and Eric too??) Idk, I've been rambling too much. Wuv uu
Uhhhhh... wow, you just wrote an entire fanfic right now uhmm...I’m impressed!!! Still, out of everything you said....uhhh..... no?
I'm afraid it doesn't quite play out that way. Haha. You see, in this universe, it's not just a simple role reversal. There's a divergence and a very different motivating factor. Imagine Gabriel with the Miraculous, but with everything turned upside down: his motive, his approach, his plan, and his actions. It's all the exact opposite. But not in the Betterfly/Hesperia way.
This is one of the most unfair and depressing AUs I could come up with (sorry). And right from the start, it’s not Adrien who suffers the most, but Eric (sorry again).
Mmmh.... I’ll give you a spoiler :)
Gabriel chose the path of evil because he wanted to SAVE HIS WORLD a.k.a. the love of his life, Emilie. This villain doesn’t want to save it, but to FIX IT. On a more personal level.
Do what you will with that info :)