I'm sure Dave says in one of the early episodes (may have been 'Future Echoes') that he doesn't care what the Earth is like now, he just has to know. I think that makes sense from the point of view of a man drifting through space millions of years in the future. Lister basically has two long-term goals; getting back to Earth and finding Kochanski. It seems unlikely, given his current situation, that anything more pressing will change those goals. On a ship with a crew of four, he's not likely to abandon those dreams in favour of setting up a tailoring business or getting a job as a bank clerk and working his way up the vocational ladder. For now, the show just needs him to not be lacking any hope, so that he continues his steady journey through the cosmos having adventures. An end to the whole thing doesn't have to involve achieving those goals, it could be anything at all. Perhaps Lister will find out Kochanski has met someone else with whom She's very happy, and move on from that dream, maybe finding someone new himself. Perhaps the crew will find humanity has abandoned Earth to the rat people, and set themselves up somewhere else. Satisfying endings to stories like Lister's are rarely what the character hopes or aims for. But an ending is still an ending, and who needs it to end? I'm now grateful for every extra series we get, but I wouldn't mind if it's left where it is. But I don't think I'd want a definitive ending now. I have someone like that. I met up with her in November last year for the first time in seventeen years. We've been an item since new year. She's more amazing now than ever. My memories and dreams didn't do her justice.