the theory that Maul could return was the fact that in Dark Forces II (good game btw) there was one bad guy 'Maw' ->'Maul' cut in two... he returned to the game, well 1/2 of him...
But GL said that under no circumstances Maul would return , he said Maul was mauled; cut in two so there were no doubts around him.
I think that there is a new apprentice in EpIII but Anakin kills him