We're talking fundamental breach of contract here, and not from anything you've done based on what you're telling us, so my response would've been:
"Then how many breach of contract suits are you currently involved with?"
I can't even imagine, based on the situation you described, that you would want this stress on an ongoing basis. If you think your reputation would be ruined by firing the client, imagine the one you're getting being walked over by the client, it's a double-edged sword here.
Don't get me wrong, I'm nice to people until push comes to shove, and we would've been having this "contract meeting" the first time a couple of weeks went by without getting content from the client. I always send a notice under these circumstances that basically states "the contract obligations and deadlines cannot be met as the client supplied materials have yet to be delivered" and let the chips fall where they will.
Hopefully you'll get the client to come to terms for content delivery at their meeting.
If they won't give you what you need, at least you know where you stand.