My natural hair color is dark brown.
I have been bleaching it blonde for about a year and I liked it but I though I would try a darker blonde. I bought clairol nice and easy in natural medium champagne blonde. Instead it turned this light reddish brownish dark blonde and I hate it. How long before it starts to fade? What color will it fade into? Before I was using a bleaching kit for my roots, can I go back to using that once this fades, or will I have to re deposit a blonde color?

You could wash your hair often and it'll fade faster. Use Clarifying Shampoo and you can let it sit for 10 minutes and it'll help it fade for you.
If you do this it could fade to a more redish color, If you are wanting to go back blonde then you will just have to highlight your hair to the blonde color you were before!