[quote=@The 42nd Gecko]
Hmm... If Artoria and everything she ever did was deleted (everyone's reversing the transfromations), wouldn't that mean Ira and Victoire would still be in Hildr's clutches?
[/quote]

Actually, it's just as I mentioned before. People are sure that these things happen and that [i]someone[/i] did it, but no one can remember who was it, no matter how hard they try. This includes any recorded proof of Artoria ever existing, and any thing at was unmistakably hers ceasing to exist as well, but —for example— if she had a child, said child would keep on existing, but be utterly unable to recall anything about their mom.

Really, it's just like what happens when one's Power of Existence is totally consumed on Shakugan no Shana. The world itself simply refuses to acknowledge that you existed, but causality can't be reversed. Or so it should be.