Ending was just flat out dumb
The idea that he just got so pissed off at being "pranked" that he just decided to disappear is absurd. This is the same guy who was dead set on finding out what was going on. Thing is, there wasn't a hell of a lot going on. He didn't uncover some amazing secret or witness something spectacular. He just saw a bunch of rich people hanging out. They then find out he snuck in and decide to prank/scare him. He then gets furious because he obviously can't take a joke. Or perhaps the prank was just so terrifying he was mentally scarred forever. In the end, he was so mad/scarred that he decided to go climb into a black hole, never to be seen again.... Right.
That was a hell of a prank. Even incorporated the wife and kid just to really put that prank over the top.
That being said, anyone with a brain would immediately conclude that he was killed. If this secret society was intent on releasing info (as had been said) but not enough to let us truly form an opinion one way or another, they completely botched it. If you took 10 people, I'd bet 9/10 would agree he was killed.