Screenwriter David Milch announced back in November 2017 that he had finished a script for a reunion/finale movie, and HBO began reaching out to former cast members asking for availability.
March 2018, Timothy Olyphant is asked about it on Watch What Happens Live, and definitively responded that it's "never going to fucking happen".
Well...
Spoilers for Fear The Walking Dead
Spoiler: show
They need to get this ball rolling while Ian McShane is still capable of dropping f-bombs.