Thats for sure ! Even Blizzard stated that "we are bringing him back" when one of fans asked about Villains bodies like Arthas and Illidan. Blizz stated that Arthas body is being buried somewhere but Illidan is most likely coming back so ....
Edit :
During the Blizzcon 2010 World of Warcraft Quest and Lore Q&A panel, Chris Metzen was asked about the possibility of Illidan being revived or redeemed, and Metzen replied that it was something he would really like to do and that he is a sucker for a good redemption story.[12]
At the Blizzcon 2011 World of Warcraft Open Q&A panel, Metzen was again asked about reviving Illidan. He asked the crowd if it was something they would like to see, the crowd exploded and cheered in response, and he said they would work on it.[13] He later revisited the topic during the World of Warcraft Lore Q&A panel, after being asked about the dead bodies of important villains. Metzen indicated that based on fan reaction they would most likely bring Illidan back, and would have to decide on a way to revive him, noting that his corpse would be very significant.[13]
12
http://www.wowhead.com/quest=28257
13
http://wow.joystiq.com/2010/10/22/bl...anel-liveblog/