It could cause short-term shocks, but I feel like over the long run things would recover.

If the advertisers thought they were paying $500 for 10000 clicks resulting in $1000 worth of visible revenue, the fact that they really only got 5000 "real" clicks resulting in the same $1000 worth of visible revenue doesn't really change the equation much.

Over the long run companies spending money on advertising are going to hone in on how much they can spend compared to how much revenue they get can trace back to that advertising spend.

The pay-per-click model and the current cost-per-click pricing is just an implementation detail of the current state of web advertising. Advertising still works when those stats aren't available, like in Podcasts.