Personally, I think finding the author of the book, and asking him/her to give villains happy endings is opening up a whole huge can of worms.
Meaning, that book has no stories from Storybrooke. They’re all from the Enchanted Forest, before Regina cast her curse and before Regina’s redemption. As far as I’ve seen, the characters in the book are 100% different than the characters we know from Storybrooke.
As a redeemed woman Regina’s happy ending looks completely different than the happy ending the book’s Regina would want.
If the story was changed, and villain Regina was given her happy ending, wouldn’t that ending be a dead Snow White, and Queen Regina with total rule over her kingdom? Wouldn’t Maleficent’s happy ending be a dead Queen Regina?
And, let’s say we go with present day characters. What would the evil Snow Queen perceive her happy ending to be.
If you assume the author is a good guy, you could assume he/she might write some sweet tender happy endings. But, what if the author was himself a villain. Maybe he’d write some creepy evil yummy happy endings where all the villains live happily, evilly ever after.
Not sure where I was going with this. I just don’t think this will be as simple as Regina thinks it might be.