Did Hermione ever fix her parents' memories?
At the beginning of the 7th book, Hermione Granger Obliviates her parents' memories of her and themselves and makes them think they want to move to Australia.
Is there a fix for this type of spell?
Did Hermione ever recover their memories and return to them after Voldemort was defeated?
The book didn't say she used Obliviate, just that she modified their memories. According to this quote from JKR, there's more than one type of memory charm.
Actually, there is in-book proof that she did not use obliviate! In the scene where the three are attacked just after leaving the wedding, she wants to modify the Death Eaters memories and mentions she never used obliviate before.
@LarsEbert You should add to this with the exact reference. I believe this is better than the accepted answer.
It may be worth noting that no one for several five years was able to cure Gilderoy Lockhart (I'm certain some fanatical and gifted witches would have given it a shot), who was exceptional with confundus charms. It's hard to compare his ability to Hermione's though, it'd be like a race between superman and the flash.
Probably, I mean they're her parents. Why in the world would she keep them with no memory of her and wanting to move to Australia?
I'm sure she must have, but it's not talked about in the books. It wasn't a big plot point in the books, it was just mentioned in passing, although in the movie, they made a bigger point of it, likely for the high emotional feeling during the scene.
Hermione cared very much about her parents. She had to obliviate them because she didn't want them to get killed during the war, and made them want to move to Australia and have new identities instead of being Grangers. She was powerful enough to reverse any charm she put on them. No doubt it took her a while to find them after the events of the book, but I bet it was near the top of the list of things for her to do. In fact, in Chapter 6, she says the following:
I’ll find Mum and Dad and lift the enchantment. If I don’t—well, I think I’ve cast a good enough charm to keep them safe and happy.
And, even more proof, here's a web chat with J.K. Rowling right after the release of the book:
Maggie Keir: Was hermione able to find her parents and undo the memory damage
J.K. Rowling: Yes, she brought them home straight away.
@Kalamane - She was one of the brightest witches of all times! She surely would have used Android! \**duck and cover*\*
@Suchi, she knew their new names (Wendell and Monica Wilkins) and quite likely knew where in Australia they were going to move. Finding them wouldn't be hard.
Surely she could've just cast a spell to find her own parents. It's not like it would be hard, given that she has ready access to their own flesh and blood in herself. Or, as several people suggested, she could just google for them in Australia.
I wonder how they reacted. And people around them, both in UK and Australia. "Oh hey we made friends and great jobs", nope you gotta forget and start over, bonus unexplainable stretch marks form pregnancy that never happened, "oh hey we made new friends and new jobs", NOPE you gotta start over AGAIN. God damn it Hermione.
And in answer to Hermione again in interview with JKR. "Laura Trego: Did hermione really put a memory charm on her parents she says she did but then about 50 pages later tells ron shes never done a memory charm
J.K. Rowling: They are two different charms. She has not wiped her parents’ memories (as she later does to Dolohov and Rowle); she has bewitched them to make them believe that they are different people."