The show is not cancelled officially by FOX yet. If ratings miraculously improve for the "finale" they might revive it.
Only after FOX decides will we hear about the show's fate on another network (most likely Showtime, possibly ABC). I think it's more likely that not that AD will return. The show is selling a ton of DVDS.
http://the-op.com/phpBB2/viewtopic.php?t=2798
The Showtime deal isn't dead, nothing regarding the Showtime deal dying has been posted from an official source. The last we heard, Mitch was mulling it over and Showtime were still waiting for Fox to cancel it until they could pick it up. The president of Showtime has said in interviews that they're very excited about Arrested Development and would love to pick it up, so unless Mitch decides not to or Fox does something, we can only assume the deals are still in progress at the moment.