My timing belt has slipped, does this always cause valve and/or piston damage?

What is your question?

I was hearing a little squeek, like a belt was loose, after turning my car off I couold no longer start it. I hadn't had any trouble starting before this. A friend hooked up a diagnostics tool and no codes showed up. A mechanic looked at the car and said that the timing belt was definately the issue. He said he would have to do some research to find out if this caused valve damage, he was going to check one of his "books"