In this sense they are following a similar path as Bebo, where I worked before they were acquired by AOL. Launch viral product to teens, blow up huge, score huge business deals, and then growth stagnates because it turns out the original vision only encompassed a product, not an entire platform. Bebo ended up selling to AOL right before it became clear the entire business model was failing thanks to Facebook. I saw a comment below about 2019 being the year that Snap is acquired. I could very much see that happening.
The only thing that would turn things around is if Spiegel can pull another rabbit out of his hat and launch a category-defining product somewhere. Augmented Reality could be where they do it. They did fail miserably with Spectacles, their first take on smartglasses, but again, give credit to them for having the balls to invest in hardware and ship a product. That said, the fact that they shipped a v2 of Spectacles that didn't fix any of the core problems with the original isn't a good sign.
Still, augmented reality is going to be the future of computing when it merges with consumer wearables. It's early days in this market. Every Big Tech company is racing to launch the iPhone of smartglasses. Snap has managed to be the first to launch consumer glasses with a camera. If they can pull their sh*t together and ship something that is actually useful and doesn't look ridiculous, they could still emerge as a dominant player.