I would be very surprised if they kill off Duke because Hasbro has spent a lot of years and money making him the poster child for the line.
The rumor seems to stem from the fact that Tatum is shown in the dessert and then after the attack it's said that they're all dead. That seems to imply that Duke is dead also, even though we don't see him. But, we also don't see him any later in the trailer either.
In RoC there were a lot of unnamed Joes running around the Pit and it may be a similar thing this time in the dessert. It's kind of implied that the Joes from RoC (Breaker, Ripcord, Scarlett, Heavy Duty, etc) could be dead from the trailer but since they aren't named, I think it would not be in Hasbro's best interest to kill them all off. I'm wondering if those Joes, and others, could be off-screen and jailed as renegades or scattered and that's why we don't see them. Plus, the Joe roster is so huge, even without killing them, we could never see some of those characters again on film and still have a great pool of people to add to the team later. Gung Ho, for one!
My final thought on Duke; since RoC didn't use the disfigurement storyline on Snake Eyes, and assuming Chu didn't change that, Duke could be all messed up in the attack but ultimately survive only to be recast after his miraculous recovery and extensive plastic surgery and looking strikingly like Sam Worthington. Or Tom Hardy? Maybe Cam Gigandet? I'd take Ryan McPartlin also.