>For the Facebook ponzi scheme to fall apart, the ads have to stop working.

I am taking the Ponzi scheme here refers to numbers of users? Because for Facebook's Client, it is obvious that Ads is working and bringing a positive ROI. And these ROI are not paid out directly by Facebook ( which could easily distort the number ) but results measured through other channels. Which means from Facebook's clients perspective it is not a Ponzi scheme at all, as there is nothing to lose from its Client.