Well, this is old..
Did the paranormal debunker meet his end?
Yes, and no.
So, originally as shot, yes, as the director (and the tie-in book writer) reveals that they shot a chalk outline of a body on the street floor, usually indicating that someone (in this case Heiss) died there.
But as noted below, this was changed in post-production, so that it was left ambiguous, and then later, not so ambiguous as they add a NYP article that says the character was hospitalized - showing he survived, and then the tie-in book has a foreword re-written by the then-recovering Heiss.
I came across this:
Suddenly, Mayhem manifested, flied out of the Trap, carried Heiss through the window and Zhu's sign, and dropped him onto the street below.
Kevin remarked he went out the wrong door. Holtzmann, Patty, Abby, and Erin ran to the window and looked.
Holtzmann broke the tension and remarked he wasn't really Ghostbusters material.
The police ruled it a freak accident but continued investigating.
Heiss was hospitalized.
Heiss paid thousands of dollars in out-of-pocket medical expenses and spent many months in physical rehabilitation.
Heiss later wrote the new foreword for the revised edition of Ghosts From Our Past.
In the Trivia section of that page:
Heiss was going to be killed off. A chalk outline of Heiss, his hat and cane were even filmed but deleted. It was decided to keep what happened to Heiss ambiguous.
In one of the movie's tie-in books, "Ghosts from Our Past: Both Literally and Figuratively: The Study of the Paranormal," from Three Rivers Press, it is revealed that Martin Heiss survived the fall, but was very severely injured and went through months of expensive physical rehabilitation recovering from his injuries.
Andrew Shaffer originally wrote the new forward for Ghosts from Our Past: Both Literally and Figuratively: The Study of the Paranormal from the perspective that Heiss was a Class 4 ghost. During post-production of the movie, Heiss's status was changed to be vague. Shaffer modified the forward to reflect he survived the fall but forgot to change a joke on page 17 about him being a ghost.
In the movie, Martin Heiss was ejected from the Ghostbusters' window by Mayhem and it was played off vaguely if he survived or not. Looking at the revised Ghosts from Our Past (GFOP)'s new foreword by Heiss, it appeared he survived after months of recovery but in the third paragraph on page 17 - it is stated by Abby and Erin that they got an actual ghost to write their new forward. Was this a mistake or intended as a joke that Heiss isn't aware that he died and manifested as a ghost?
ANDREW SHAFFER: During filming, there was a chalk outline of Martin Heiss on the street, indicating that he'd died from the fall. Armed with this information, I wrote a foreword from his perspective—as a Class IV ghost.
However, during post-production of the film, Dr. Heiss's fate was altered to be vague (leaving the possibility open that his character survived, for potential sequels, I assume). So I changed the foreword to reflect that he was alive, but unfortunately missed the joke about him being a ghost on page 17. That will be corrected in future printings of the book.
And from the extended edition:
New York Post (2016). Ghostbusters (2016 Movie) Extended Edition; Chapter 12 (2016) (Blu-Ray ts. 1:27:50-1:27:52). Sony Pictures. New York Post reads: "Two days ago, paranormal skeptic Martin Heiss was hospitalized after falling through a window in a freak accident."