Here be spoilers, beware (they aren't detailed but heck, y'all know the drill)
- The issue begins in the past with T'Challa receiving a ceremonial knife from his dad
- The Illuminati explain to Steve Rogers that they have a plan to remove the Cabal. Namor explains that he did what he had to do but it was wrong and he's ready to answer for his crimes.
- The Illuminati pretty much accept whatever consequences come their way as a result of their actions, except Black Panther who bluntly refuses to turn himself in.
- Reed explains that there's another Incursion about to happen but its a dead planet thats coming towards the Earth. Namor is to make sure the Cabal are there when it happen.
-Namor stands with the Cabal on the dead planet but Thanos notes there's been an event and their timeline grows shorter.
- Issue goes back in time where T'Challa is giving the ceremonal knife to Shuri as it belongs with her as the queen of Wakanda.
- Reed explains to Rogers that they intend to blow up the planet with the Cabal on it to pretty much end them. Namor agrees as this will be his last act as a free man.
- Issue flashbacks again to Wakanda where Shuri returns the ceremonial knife back to T'Challa as she gives up what's left of Wakanda to him
- On the dead planet, Namor arms the anti-matter bomb but as Namor is flying away. T'Challa confronts him with the ceremonial knife and stabs Namor in the chest. Then Blackbolt screams at Namor and and knocks him down. Namor falls from the sky (they were on a floating platform) and lands on the dead planet. T'Challa notes that Namor's biology and genetics makes him incredibly resistant to damage but Blackbolt's scream and the fall (from the sky) will take him down for a while. T'Challa says he wants him to be aware of what happened and will spare him a few minutes because he wants Namor to know there's no forgiveness for what he did and wants him to know that it was him (T'Challa)that ended Namor.
- The dead planet is blown to bits with the Cabal on it. Rogers asks where's Namor, T'Challa replies- he's not coming. So ends the Cabal.
First things first, I don't think that Anti-matter bomb can kill Thanos. Secondly, I don't even think Namor is dead, granted the odds are against him surviving, in comics, anything is possible.
But full credit to Hickman, Time Runs Out is probably one of the most gripping superhero storylines that I've followed in years and is the best going on in comics at the moment IMHO.