Supernatural succeeds where various franchises and science fiction movies have failed. As extended universes get larger and larger TV shows and movies have come to up with ways to connect these characters together and Supernatural just hit the nail on the head.
Everything can be explained away using the multiverse theory. Including but not limited to: Time travel, Sam & Dean dying multiple times, other characters coming back alive, and unstoppable apocalypses that were stopped. Sam & Dean are powerful deities in themselves. They apparently have the power to transcend the normal flow of time. That fits in perfectly with the multiverse theory and shows like Star Trek which have featured characters like Sam & Dean before would agree
From the very beginning of the series, Supernatural wrestled with the idea that monsters are real. Even though, the world at large seems to be unaware of this, one can only suspend their disbelief for so long. How is it that more people are not aware of the supernatural goings-on in small town America? Except for a few small town cops and hunters that Sam & Dean keep on payroll, no one else seems to be aware. Why? If the monsters from Supernatural are supposedly these world-ending deities from real Earth-lore, with desires to control the world, like they are in every season arc, then I would assume more researchers would be figuring this out. Especially since Lucifer just took control of the President of the United States not too long ago.
So perhaps a form of the multiverse theory works here. Maybe something from the multiverse is shielding people from looking under every rock for things that go bump in the night. In Supernatural’s Season 13 fall finale, the TV show introduced us to a much larger multiverse than we’ve had. It should be clear by now that Heaven and Hell in the show are other realms, other realities, and perhaps universes. Along with various endgame scenarios and apocalyptic visions from Hell that monsters like Azazel wished for and created.
With Jack’s powers he has access to multiple dimensions. We could see a number of universes in his mind. Sam & Dean are flung to another monster/dinosaur world, and Jack gets thrown to a universe that’s been called, The Bad Place. So now we’ve got two more universes and in Jack’s dreamwalk we see a ton more. Also let’s not forget about Castiel’s The Nothing. We’ve also been to a world in which Supernatural is a TV show, as well as indirectly The Land of Oz, and various time travel episodes all hint at other realities. This indicates that Supernatural-TV-Show-world is the real world and not Supernatural in the TV show. So if that’s the case, then why or what is keeping people in the dark on Supernatural?
So while seemingly solving one problem in the long running series, Supernatural has now opened another can of worms. This will be full of potential for the future of the series. With all these universes available to them, how will Supernatural deal with them?