Twenty-nine years after their pioneering observational doc series entranced PBS viewers, the filmmakers Alan and Susan Raymond are bringing back the Loud family one last time. They are talking with WETA about offering the new hour-long episode to PBS, according to Mr. Raymond and Jim Corbley, v.p. of production management at the Washington station. If a deal is struck, the film could be ready this fall, Raymond said. The occasion was the death Dec. 21  of Lance Loud, eldest son in the Santa Barbara family, who stunned his family and became a symbol of gay liberation in 1973 by coming out on national television.