There is no evidence that Moiraine or Lanfear are dead. The doorway was thoroughly destroyed, but that just means that they're trapped. The creatures want to make bargains, so they have no incentive to kill out of hand, and as Moiraine had the bracelet-angreal when she went through, she may have been able to fight Lanfear effectively. There's also one other thing: Min's vision saying that Rand would lose Tarmon Gai'don without the aid of "a woman slmost certainly dead." It seems likely that this refers to Moiraine, especially if you think of Min's reaction to the sight of the rebel Damodred they met in the forest, whose name happens to escape me. Wouldn't Rand's being ta'veren work to help Moiraine if he was going to need her later on? And while Lan says that he cannot feel her, Moiraine could have done that with a bargain with the foxes.