Mr. Leet did not make it clear that you die. He made it clear that it will consume your life - trying to learn the truth ... and the "mystery" of what Indrid Cold is is not left up in the air and is in fact partially explained, by Mr. Leet nonetheless ...
Here's the deal. Mothman is not alone; there are others. Whatever they are, they know of the world beyond death and of time; they know the future, they know our thoughts, they know the "dark side." Mr. Leet said - if they find out that you know they WANT to communicate through you because it is RARE (he said this) for anyone to notice at ALL. the fact that you notice makes you SPECIAL - it will drive you mad/distract you (as it did his wife) or they will REACH you and bring you to the other side. maybe you'll be happy there's something more beyond death, and that's the gist, which, ironically, the movie Dragonfly is also touching on.
Because, the nature of pov - we SEE his wife and Gear DOESN'T. Sure, the mothman can pretend voices (over the phone) but he has never pretended appearance. that was his wife that passed him on the street and walked into the precinct to talk to the blonde chick.
What I got was a sense of creatures whose motives we don't know - they could be good or bad - but, regardless, they want to COMMUNICATE - and they keep trying, but obviously, what they know can pull someone out of our world and into theirs - in a way, a theft. But, if what they say can HELP mankind, can reach him on a level that most men are not capable of because of whatever (weakness, deliberate blindness, etc) can take you to a realm and level above and beyond the corporeal or whatever, is it worth it?
In Gear's case, I would say it was. You have to learn to play the rules - Leet learned that he couldn't, and that to live free of it he'd prefer to pretend to ignorance. So would the blonde cop.
As for the temporal lobe thing - one wonders if someone could withstand knowledge without that death. Gear and Will Patton weren't the only ones who saw it. Everyone in that town saw it - do they all die of the same mysterious brain tumor? i don't think so. they choose to blank it out, yes, and live. but there's a question of whether, if you DON'T choose to blank it out - will you definitely die, or are they looking for the person who can withstand the communication, the knowledge, the person these beings want to communicate through?
sure, it's true, maybe Gear wasn't that person and would just pop a vessel. or ... maybe not. i guess ... in a way, I'd rather know. i'd rather know what i must face than hide away from it. if his wife is walking around and existing in some form - and was "taken" by this thing, I'm sorry, I don't care how loving the blonde cop is, I've got the proof, I'm not going to betray my wife and that love to cling to ignorance so we can all be happy and live the happy life. i'm going to face it.
and that's that.