Wikipedia says her disappearance was addressed in the fourth-season premiere: http://en.wikipedia.org/wiki/Alana_Mareva
Yeah, Alana presumably lived out the rest of her life in the past, which gave her character closure of a sort--which is why I didn't feel compelled to reopen that can of worms after she had already been written out of the series. If the series had continued . . . who knows? There was certainly potential for some kind of time-travel storyline that would bring her character back.