In 1996, Mumy and his Lost in Space costar Jonathan Harris were reunited at a Walt Disney convention in Orlando, Florida. Mumy worked again with Harris on the retrospective special Lost In Space: Forever (1998), where they reprised their roles in a scene written by Mumy (Harris rewrote his own lines).
This occurred the year after the rest of the cast (including both Mumy and Harris) stated in a TV Guide article that the Sci Fi Channel planned to do a Lost in Space marathon while promoting a new film. Harris was to appear in the planned television film Lost in Space: The Journey Home, but died before production was scheduled to start, in 2002, and it was subsequently cancelled.