He'd still have access to his books if he'd installed the Kindle desktop application and had synced all of them down to his desktop.

In fact, something is a bit weird here, because whatever books were on the Kindle itself should still be there. There's no mention of it having been remotely wiped.

Edited to add: I don't want to minimize this issue, though. Because being locked out of your account means you can't buy books or grab the freebies that pop up. Right now I'm suffering a bit like that due to account confusion I need to resolve with Amazon. Seems I have an older account they won't delete and from time to time Amazon gets confused and sends me to it -- and the first time that happened, I thought all my books were gone (the older acct never had books). A phone call straightened it out. And now I must do that again.