What a great story! I haven't read the original, but I love the structure and how you've woven bits of canon into it - Victor telling Albus about Harry, the Prewetts dying, and the gradual revelatation of who Mara is (both in relation to Victor, and in canon). I've thought for a while that there should be more time travel stories in HP and this is a wonderful example of how that premise can make an unusual pairing work.