Jedi News reports that the latest rumor regarding Star Wars: Episode VII is that Ian McDiarmid will return to the franchise.
While the details of the role aren't known, it seems likely he would return to play Palpatine again. Palpatine came back as a clone in the expanded universe comic series Dark Empire, so that's one possibility as to how the Emperor could be back from dying at the end of Return of the Jedi.
Until Lucasfilm confirms the story, it should only be taken as a rumor for now.
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