Once upon a time, Princess Annwyl was ten. And she was writing an Indiana Jones fanfiction; she had already written one, and it had been her first novella, so she was quite proud of it.
Well, she quarreled with her brother, and then left the room to go get a drink. When she came back, she found her brother had deleted at least a chapter's worth of writing.
So yes; I have had to rewrite things from memory before. Sadly, this was so long ago (coming up on seven years now.

), I can't remember if it turned out better or worse.
Don't worry!

You might still gain back what you lost of your writing; even if you don't, I'm certain you can write it just as good as or better than it was before.
Don't keep your chin up - keep your head bowed, in prayer to God. Whatever happens, you still have Him. And you always will. <3