The Darko Sequel is only a sequel by name. Richard Kelly [Donnie Darko director] has gone on record saying it has really nothing to do with his film, and none of the original crew are involved.
And, the original cast IS involved. Daveigh Chase is going to be Samantha Darko, like she was in the first film.
Info:
http://www.imdb.com/title/tt1231277/