Wiki states it ran for two yearsbut doesn’t say specifically how it ended . It implies the earth people did not get off the giant planet.
The episode guide in the wiki pretty much explained it. It was canceled, as all series, with a rare exception, were back then. Other than “The Fugitive,” the concept of a series finale was pretty alien.
Side note: Supposedly, in one episode, a cast member calles actor Kurt Kasznar (Commander Fitz-Hugh, the “Dr. Smith” counterpart) “Kurt” instead of “Fitz-Hugh.” Somehow it slud by.
This comment sums up the last ep of LOTG nicely.