Cynthia Watros, who played the character before she was killed off in the second season, will return this year, said Carlton Cuse and Damon Lindelof.
"Finally, all of your questions (about Libby) will be answered," Cuse said.
But he producers said that not all of fans' questions will be answered, with Lindelof claiming: "That would be too pedantic."
They also admitted they have known the final image of the mythologically dense series about Oceanic Airlines Flight 815 since the first season, although Cuse said the last episode hasn't been written yet.
They said the episode - to be aired in the US in May - promises to be challenging, with actress Emilie de Ravin revealing she had to read the script three times before it made any sense.
"Get ready to scratch your heads, America," Lindelof said.
The producers are hoping that final show is something that will be talked about afterwards in much the same way as the diner scene that ended The Sopranos.
"I don't think it would be Lost if there wasn't any arguing and active debate among the viewers about whether or not it was a good ending," Lindelof said. "My mom will say it's a good ending, even though she doesn't understand the show."
The actors, meanwhile, said filming the series has been an emotional journey. "I'm going to cry like a baby when this series ends," Evangeline Lilly said.