So we've known for a while that Ronnie Raymond would not be a main character in DC's Legends Of Tomorrow, while Dr. Stein would be. So the question fans have been wondering is "how's Firestorm gonna work". Now thanks to a quote from Legends showrunner, Phil Klemmer, we now know how Firestorm is gonna work. When asked about Jay Jackson Klemmer responded with this....
"I will say he's probably the last person that Professor Stein wanted to share Firestorm with. I think for me it's all about tension and interpersonal friction, so this isn't the normal superhero story where everybody's on the same team, pushing in the same direction; it's really about us sort of turning on ourselves and whether we can learn to get along in order to save the world."
So it appears that Ronnie will not be a part of the Firestorm Matrix by the time Legends begins and that Jay Jackson will be taking the role Jason Rusch had in the comics. What happens to Ronnie is still unclear, but many have speculated that Ronnie will sacrifce himself to close the wormhole in the next episode of The Flash. Klemmer also revealed info about other characters and storylines including that Captain Cold may try to rob a bank in the 70's, Ray Palmer/The Atom might try to change the past to bring back his dead fiance, Rip Hunter will be in every episode and that other "Time-Masters" would appear on the show, some characters will be left behind in different time zones and some characters will betray the team.