Hey Spanty welcome to SR.
I am a recoverd heroin addict and the loved one of an addict so I have been on both sides. Instead of worrying about what could happen in the future, spend the time now getting healthy emotionally and physically. Start deciding what kind of boundaries you want to put in place not only for her, but for other people in your lives also (a person doesn't need to be an addict to violate our boundaries). Try to get yourself in a comfortable place where you feel like you are thinking straight and then no matter what happens, you will be able to handle it.
As for your fear she might not come back, that is completely up to her. As a recovered addict who moved 12 hours from my home state I can say that sometimes moving away is the best thing for the recovered addict. Being home held way to many memories of using drugs and all the people I knew and associated with drugs were always around. I got tired of being tempted by memories at everywhere I looked so I went far enough so that when I got a craving I couldn't jump in the car at 2 am and drive back to meet up with people. If that time comes, you will have to respect her decision. Only then should you start worrying about the different outcomes such as long distance relationship, breaking up, moving there with her, etc.
Try to just be in today and enjoy the little things that we too often overlook. SR is a really good place to vent and get adivce from people who have been there and gotten past it. Knowing that you're not alone also helps alot since when dealing with an addict it gets very easy to think that you are the only one that has to deal with this.