Madge should have lived so that she and Gale could have had the best background haters to reluctant acquaintances to besties in denial to lovers relationship.
Then Katniss gets to have two people to talk to about her Peeta problems and when she's like "IDK if I love him 😕" and Madge just smiles cause yes, you do, but imma let you figure it out on your own time. And Gale just rolls his eyes and walks away cause ffs Katniss, you idiot, go get your husband.
And then Katniss, instead of having to deal with Gale's bullshit in MJ, she gets the pleasure of watching her besties fall in love with each other in real time and she's trying - horribly - to give them relationship advice. Also that one part where Gale's like "I think Finnick likes you" it's out of genuine concern and not jealousy and then Madge laughs her ass off cause "no he doesn't Gale, he misses his wife and she misses her husband and they're best friend bonding over shared trauma". After that, Gale's jealous of Finnick - not because he thinks he loves Katniss but because bro, that is MY bestie get your own.
Also, with platonic bestie everthorne, Prim's death is that much more heartbreaking. Now, instead of being someone that Katniss is mildly annoyed with consistently because she doesn't know if she loves him or Peeta, they're best friends. She tells him (and Madge) everything and she loves him (platonic). And then, she goes from having him as a constant to not being able to look him in the eye and being devastated knowing it wasn't really his fault but she can't seperate him from that event. They grow apart, and, by extension, so do her and Madge.
But because I like happy endings, Gale and Madge move to D2 and Gale tills part of their backyard so Madge can grow a garden and there's a whole section for strawberries. They get married and have a few kids and they're happy. And they make regular trips to 12 to visit Gale's family and also Haymitch (who has lowkey had a soft spot for Madge from afar her whole life because of her icon of an aunt).
It takes a few years, but Peeta and Madge meet each other at the bakery one day and spend a couple hours catching up. Peeta tells Katniss, who then (she denies it) comes with Peeta to the bakery "to help" (to maybe catch Madge). Madge comes by and they reunite and Madge speaks on Gale's behalf about how awful he feels, but she tells Katniss that she understands why she can't forgive him. They decide to remain friends.
The Hawthornes visit 12 a few more times before Katniss decides she's ready to see Gale again. They meet up (with their spouses in tow so they don't have to be alone) and he apologizes and she maybe slowly starts to heal a little more. As a little more time passes, she forgives him for something that wasn't technically his fault and they all become best friends again just in time for Gale and Madge to be the first toast baby's honorary aunt and uncle.
They all stay besties till the very end and their kids are besties and Haymitch is Grandpa Haymitch to the Hawthorne and Toast babies and they all live happily ever after the end.
