The aesthetics of the Western are dead for all non-nostalgic purposes, but the storytelling conventions of Westerns are alive and well. If you think about the story of most Westerns. You're in an area of the world far from effective law enforcement surrounded bandits and businessmen willing to kill for their piece of the pie. The protagonist is a self-reliant man who does what he feels like without social restraints, and only gets away with it because he's strong and skilled enough to beat anybody who challenges him.
These conditions make the perfect crucible for character driven action drama, and we see those elements in all kinds of science fiction settings such as Firefly and Cowboy Bebop.
The Western is alive and well. It just doesn't take place in the 19th century American West anymore. Train robbers are space pirates and Indians are aliens.