If I were to activate a book a year later or even a month later I'd probably just photoread it again to help with the activation. Afterall photoreading doesn't take long.
Is it deleted. You didn't really have it in the first place if you didn't use the information in the book. Becomes a bit like breakfast, How important is it to you to remember what you had for breakfast one year ago today? For many people photoreading one book is as much time as they spend having breakfast. 
Will activation be more difficult after a year. Depends if you have worked with other books on the same subject, probably not. If not well you might find yourself having to take a couple of extra activation passes. Just as easy to give it a refresher photoread. Even with regular reading a novel can seem new to me in parts when I read it again a year later.
Alex
