I think there is a distinct possibility of that happening. However, if it does, I don't see it being niche forever. As much as we bash on the MCU here, it has brought comic books back into the positive mainstream consciousness.
Wrestling, on the other hand, has always been an innovator in Television, predicting and setting trends for decades. Wrestling built WTBS, which is what all modern television stations are modeled after.
Wrestling is also the first to prove that there are people willing to tune in week in and week out to watch a never ending story.
And even then, there are few programs that get a steady, reliable viewership like wrestling. TNA proves it.
And ignoring that, the amount of Independent promotions in the US alone shows just how big the fanbase really is. Yeah, attendance varies from 500 to 15, but it all adds up to something greater than the sum of it's parts.
Sure, one day it might all go away, and WWE will have only it's hardecore fans, but if someone had the ability and business sense, the town could be put back on the map, and be bigger than ever. You can count on that.