"Jack devises a plan to do away with "The Others" once and for
all, Sayid uncovers a flaw in "The Others'" system that could lead to
everyone's rescue, and Charlie's dangerous task may make Desmond's
premonition come true."

This episode is Charlie-centric, but sadly this may be the last of
such episodes... In other words, (although I question whether the
writers would make this so obvious), everything leads to the fact that
Charlie will die:

1) The episode title, "Greatest Hits" refers to an album containing a
band/artist's top songs, usually after a member(s) of the band or that
artist dies. With Charlie being a member of the band Driveshaft, you
can see the connection.
2) We already had an episode that teased us from the opening scene
that Charlie would die, but he survived in the end. If he doesn't die
in this episode, it will be as if we've seen it all before.
3) The "epitaph" in the episode description..."Charlie's dangerous
task may make Desmond's premonition come true."

Honestly, Charlie's cool, but he might have lost our interest in his
character. There's a good chance he's not coming back next season. To
dodge having to give a definitive stance on this issue, I'll just say
that we'll just have to wait and see...