I think people are making a really huge assumption here. There are three obvious answers to why Asmodean gets the "final death" according to the Dark One.

1. He COULD bring Asmodean back, but he's not going to tell Demandred, because he wants Demandred and the rest too scared to try betraying him. If he brings back Asmodean, and fits him for a mindtrap, it is still a second chance, and he does not want the Forsaken thinking they can get second chances for betraying him.

2. The cutting of the black wires might have interfered, though I thought RJ might have addressed that issue.

3. The Dark One could, but does not want to bring him back! Asmodean betrayed him and worked for the Dragon Reborn. Why does he want to give this character another chance? Note that he never says he cannot save Asmodean. He seemingly regrets his inability to get Rahvin back, but only mentions Rahvin. He never expresses regret at being unable to grab Asmodean, suggesting either that he does not care about his inability to get him or that he COULD get him but simply did not care to, and therefore had nothing to regret.

The only reason I could think why the Dark One would want to bring Asmodean back would be to torture him for his betrayal, but RJ's assertion that he doesn't care about chastisement so long as he gets what he wants from his minions would seem to undermine that idea. Why would he go through that trouble to punish a mere flea like Asmodean for his ineffectual betrayal? Sure he might give traitors a really gruesome punishment as an object lesson, but IMO that would lose some of its impact when they see a stranger being tortured, even if they mentally accept that it is Asmodean brought back.