Where will all the billions that are being poured into advertising go if there is no advertising anymore?

Why wouldn't the market regulate itself? If all web applications become premium now, there will be no space left for ads. The few remaining places might be able to receive higher prices for their ads. Higher prices for ads will mean freemium becomes interesting again. And so on...

Or there will always be freemium apps that compete with the premium apps, and the premium apps are doomed.