How this scenario plays out:
Daleks, cybermen, and weeping angels are the first to attack and also die. Most of the doctors are wiped out, but a few survive. Realizing that a few daleks are left, they team up with the doctor, go back in time, and kill all of them before ANY OF THE HARRY POTTERS HAPPENED. This would, therefore, reset the timeline, deleting the surviving battle doctors and daleks, and putting all things (except for potter) back into their place.
I don't take sides, this is obvious if you take in to mind the fighting styles of each and every person.(Side note: I love both. But think about it. The doctor could easily do the above. And he'd get away with it. Because it's wibbly-wobbly timey-wimey stuff. And, DING.) refrence