I'm a consultant too, and I've had the occasional abusive client just like everyone has at some point. And who hasn't had several clients who were just oblivious to reality?

I've kicked them to the curb as soon as possible, but not before sending them their source code (at least up until the last commit paid for), server passwords, backups, assets, and whatever else I can find.

I've never, ever, deleted anything or brought a server down just because I was angry at them. And thank goodness too, because half of the time they come back after they've had a chance to cool off.