Zachary Quinto, who played the antagonist for most of the original series, didn't reprise his role as Sylar, due to scheduling conflicts with his filming of Star Trek: Beyond. Reborn was filmed entirely in and around Ontario, Canada between April and September 2015, while Beyond was filmed from June to October 2015 in a variety of locations around the world.
Ali Larter, who played Niki, Jessica and Tracy, did not reprise any of her roles, due to scheduling conflicts.
The episode "Game Over" aired 10/22/15, one day after "Back to the Future" Day, 10/21/15. The address that Ren and Miko talk about, where the master of time and space is located, is 88 Hill Valley Road. 88 is the MPH that the Deloreon needed to travel in Back to the Future in order to travel through time and the town where the movie takes place is Hill Valley.
Gateway is 7,957 years in the future. 7-9-57 is when Tim Kring was born.
When asked about a second season on the "Heroes" Facebook page, the reply indicated it would rely on fan reception.