I don't think the collapse of advertising is necessarily a collapse of Google. Google (Alphabet, really) has so much IP and many other possible ways to grow that if crap hits the fan they can change course. Not to mention they do seem to be generating plenty of revenue to keep people interested in buying their stock. So long as Wall Street is willing to bear the weight of their ventures then I don't see Google going away any time soon. More likely is that Google eventually leaves the advertising business as it becomes less relevant to their bottom line just like how Amazon isn't about books as much anymore (they still sell them, but they got so many other revenue streams that if books as a market cratered they wouldn't go bankrupt from it). When that "eventually" will happen I can't say but I'll say I'd be surprised advertising would be relevant to them in twenty years beyond a marginal line of business.