Yelp will perish, because, unfortunately, the moral quality of the individuals isn't high and the founders/CEO seem to be blind to it.
As much as you need to be a very good business man to build a business that Yelp is, you need to surround yourself with good people, and recently, plenty of good people have left Yelp, and realistically, there aren't many out there.
I think this type of thing will be the eventual death of most social media type enterprises. People just don't realize it's hard to maintain and curate such things, worse if it gets popular. It's especially difficult when so many people just don't understand how the internet works and believe every trollish thing they read on it.
As much as you need to be a very good business man to build a business that Yelp is, you need to surround yourself with good people, and recently, plenty of good people have left Yelp, and realistically, there aren't many out there.