( "... [Dumbledore] was more than a school teacher to me. More than this I cannot say without fear of breaching the Official Magical Secrets Act or, more importantly, the confidences that Dumbledore, most private of men, placed in me." ~ Newt )
Yet, there was no mention of him in the entire Harry Potter series. At least, there was no direct mention; however, for the purpose of wasting time fan-boy-ing over this stuff, there could be a few possible clues in there.
"Harry, I have always rejoiced in my ability to turn a phrase," said the movie-Dumbledore (paraphrased); and, indeed, he usually lived up to his own hype, with reponses like "It doesn't do to dwell on dreams and forget to live, Harry."
Considering that Dumbledore measured his words carefully, one of the odd things he said -- and one that doesn't match the explanation offered in the books -- was when he screamed "...no don't kill them, please,...kill me instead," during the Horcrux hunt in the cave.
Harry thought Dumbledore was re-living the incident where Grindelwald killed his sister. This. although possible, seems unlikely because: (b) Dumbledore thought of himself as being "a shade better" than Grindelwald when it came to magic and duelling, and, more importantly, (a) based on how Dumbledore described that incident, it does not seem Dumbledore-like to ask for mercy instead of fighting and stopping Grindelwald when he was about to kill Dumbledore's family.
If Newt Scamander was alive during The Battle of Hogwarts, his suitcase could have been one of the places where Dumbledore went into hiding after "Dumbledore's Army" was exposed. If not, however, and this seems more likely to me, one of the reasonable ways he could have died could be towards the end of Fantastic Beasts: with Grindelwald killing Newt and his team, while Dumbledore, somehow rendered helpless ( unlike he the night Ariana died), pleaded him to let them live. Thus, possibly, Newt's death was the reason Dumbledore finally took on and defeated the Elder-Wand-Owning Grindelwand.
What do you think happened to Newt?
*Disclaimer (in case the name -- "Geek Mythology" -- of the section wasn't enough): this is a work of Fan Fiction / Fan Theory / Conspiracy Theory / WhatHaveYou, and does not represent- or is associated with- the original works by the famous author, J.K Rowling.