I believe you're wrong. This app won't go away like Milli Vanilli. It will last a long while until something better in the AR space comes out.
Augmented Reality and Virtual Reality are on the rise. Whether it is for gaming or for field trips and such, you'll see a massive growth especially in the mechanical engineering space and medicine.
This is Niantic's 3rd major application that has massive growth. First being Google Field Trip (smallest of the three growths but has been widely used in schools), Second being the big massive hit known as Ingress. And taking the Ingress model is Pokemon Go. Ingress revolutionized the AR space. It is massively used today and has a massive cult following with it. A lot of those members have now moved over to Pokemon Go. And why not? The game mimic's what the anime and previous games do. Go out into the world and catch pokemon's and battle them. That is the whole premise of the series and it works perfectly for this game.
Now consider this.... Have you seen Nintendo's market value before and after the release of Pokemon? They increased their value by $17B. That's insane growth! What is that going to do? It's going to support Niantic's funds to add more content to the game, hire more developers, and a whole lot more. They are already backed by Google. Niantic was once a small division of Google.
Unless there is a massive meltdown between Google, Nintendo, and Niantic, I do not see this going away anytime soon.