So here's where Sabriel is kind of an unusual book: it ends abruptly. Really abruptly. After a dramatic build-up culminating in a cinematic final battle at Sabriel's alma mater, where Sabriel and Touchstone fight Kerrigor and his zombie army, Sabriel dies.
Yep, the main character actually dies.
Should we be surprised by this? Well, maybe not. Sabriel dies at the beginning of the book, too—so maybe it's only appropriate that she die at the end. Plus, in between, this book is all about death. Turns out that dying as a baby wasn't Sabriel's time to go, but dying at the final battle isn't her time either. (Sabriel can't seem to time this dying thing right, can she?)
Sabriel's deaths add a nice kind of symmetry to the story, but after Sabriel's Abhorsen ancestors bring her back to life in the epilogue, that's it—no extended happy ending, no aftermath with fireworks and flowers. After a long and exhausting adventure, Sabriel wakes up alive next to Touchstone, and that's that. After Touchstone comments in astonishment that Sabriel's alive, she replies with some surprise herself, saying, "'Yes, I am" (E.17). End of story.
Presumably she lives happily ever after, but the more we think about that presumption, the more we're not so confident. Sabriel is the Abhorsen, after all, so it seems likely that she's got a long life of hard work ahead of her instead—though that doesn't mean it isn't a happy life, too. We just don't know.
If you want to find out what happens to Sabriel, you can always read the remaining two books the series, Lirael and Abhorsen. Be warned, however, that Sabriel herself is not the protagonist in either book—instead, the next two books are about her children. Sabriel's starring role ends here.