Does anyone have any litigation history on "celebrities endorsing something that turns out to be a fraud"?
I would think they wouldn't end up having to pay much, if anything. Their lawyers would argue "Hey, you made your own decisions! Don't blame it on Steph!"
But I would predict they make a token payment and get dismissed from the suit. Just a guess.
Edit: I don't disagree with any of the answers. I'm just curious as to whether this has ever happened before. I think "sue everyone who has any money" is the plaintiff philosophy here.