What will happen to Hiro?

Well, that future version of Hiro probably won't come about since they managed to change things at the end of the first season. In the original timeline, I believe it was the failure in New York coupled with the death of his best friend Ando that pushed him into the dark side. Because of present Hiro's time-traveling, he changed events enough that he never had to suffer such tragedies and made the world a better place.

Now, fairly recently he time-traveled into the future to see Ando blast him with red lightning. This version of future Hiro may well be dark, but he's not really the same person as the one who gave the "save the cheerleader" message. This Hiro/Ando clash may not even come about in the current timeline after numerous future-gazing in Villains that changes the way things happen.