The nature of the relationship changed the moment you became more than friends and it will never be the same again.
I would not give her the benefit of staying close via email etc because its very likely as soon as she is comfortable with that she will move futher away. I think she's weaning herself from you slowly but you are taking it as a sign that maybe she'll want to come back at some point.
I would break it off clean and lett her see what life is like without you around...that would be the best way to know for certain if she'll be back or not...kind of like ripping off the bandaid.