What happens when you deregister a kindle fire?
I have a bunch of apps and books. Will they be deleted?
They will be deleted off the device, but they are still linked to your account so you can either access them from your computer or a new registered kindle.
They'll be deleted from the Kindle Fire itself, but they will remain in your Amazon account so so you can transfer them to another device if you wanted to. Everything you buy remains in your account so you can load it on to another Kindle if yours is lost, broken, stolen, returned or whatever.