I thought Desmond was never supposed to be a major player throughout the show, and that they kept his character going because he was so popular. Now that might be mis-information but I don't think his death would be a big surprise on the freighter. Besides, all the dead folk keep coming back like Obi-wan Kenobi, Yoda, and Darthy Daddy so it's not like he would completely disappear from the show. I fully expect the last show to be a lot like the Senfeld finale' with bunches of characters from the past showing up even if it is only in a different "ghost" dimension.