The dyad would’ve been a good way to have the power in the movie without it disrupting future storytelling. Like only they can do it. At the very least, full-on resurrection could be something only they could do maybe. Guess it just depends on future stories.
As far as the movie goes, Rey doesn’t seem surprised that she can heal the snake. She just decides to do it, and explains to BB-8 what she did. Which to me signals she learned it from somewhere, and the obvious answer being the Jedi texts.
It could be an ancient Jedi ability, or it could’ve been an obscure ability Luke learned somewhere else and wrote about, since we know Luke also wrote in the texts.