Why does everyone assume that SPOILERS died at the end?
I mean sure, the camera is shut off after the burial, but that doesn't necessarily mean that they weren't going to dig them out. It's possible that they probably were going to edit the video and post it on their secret site as an example of what to expect, and ending the video like that would certainly be more dramatic and potentially attractive for those seeking the "extreme haunts".
I think it's left open ended. Yes, they could possibly have been all killed. Or maybe they were dug out, tossed back by their RV, and told that their camera's were being confiscated. For anyone looking for this particular "extreme haunt", they would be left to wonder, and apparently that would be just the thing to draw in more future thrill seekers'.
But wouldn't there be lawsuits filed against them if they let them live?
How would they be tracked down? It's an underground haunt that isn't registered. All the people participating are disguised and anonymous. The locations they use switch from year to year. You have to meet up at specific places and specific times and follow clues to get to the place, all the while the group stakes you out to make sure you're legit before they finally meet up with you at the haunt location.
It seems to me that they would be a pretty difficult group to pin down, and the argument could be made that if you went seeking "extreme scares" and then got them, it's your own fault if you overestimated your own limits.