There's only two outcomes: Either Google gets bored and kills it because it doesn't generate ten billion dollars a year in profit or it becomes so ingrained in our society killing it might cause an angry mob to attack Google HQ with torches and pitchforks.
Why it can't spin these side projects off into their own companies to survive or die on their own merits I don't know.
You're implicitly painting "become an unqualified mega-success" and "become a large scale data gathering opportunity" as if they were mutually exclusive, but they're not. It's because Maps and Mail are so wildly successful that they're great data gathering opportunities.
Wasn't that sort of the point of alphabet? To put these into their own self sustaining "divisions" so they could be spun out easily or at a high level choose to fund them?
It's actually a pretty interesting element of Google, their adherence to a centralized infrastructure must make spin offs and acquisitions incredibly difficult.
Why it can't spin these side projects off into their own companies to survive or die on their own merits I don't know.