Well when talking about Rahvin, RJ said that even though Rand baelfired him back to the french revolution (i invented the last sentence), it wasn't the death of Rahvin's soul, and he could be spun out again. I think that the fact that The Lord of the Grave can pull souls out of the slip stream is proof that they aren't consigned to oblivion. If the soul still exists, it can be spun out. If all that isn't enough for you, consider this. RJ has said that the Light's champion has been turned to the Shadow in the past. Rand/LTT is actually a hero of the horn as well as the Dragon, and he's still around, so serving the shadow does not destroy your soul. You might say that being turned forcibly doesn't count, but I think when you add everything up it points to the fact that the Forsaken before and after are still part of the Pattern.
Verin is the one who told Rand that Logain would be consumed by the Male Choedan Kal. We've got to consider this though. The oath against lying, it can be circumvented if you BELIEVE you are telling the truth. Verin is a tricky creature, we don't really know her agenda or what she really knows, but how much does she really know about saidin, or the Choedan Kal? Seriously? That was precleansing though, so it could in fact be that resisting both the taint and the flow of saidin could have destroyed Logain, but I don't think so. Rand and Asmodean both grabbed it and neither was consumed. Asmodean is weaker than Rand is now, and Rand was a lot weaker in the power back then. Really I think Logain is pretty strong. He can't match Rand in raw strength, and we don't know how strong Taim really is, but on the evidence, Logain is pretty powerful. It takes six Aes Sedai to shield him in Salidar. The one time we know he tried to break through the shield, he almost succeeded, and Siuan thinks with 5 holding the buffer, he would have. Six can hold Rand too, or at least they could in Lord of Chaos. Logain's comments in KoD seem to indicate that a gap has opened up between them as far as raw strength, but really, I think the only two non forsaken who can match him over overwhelm him unaided are Alivia and Taim.
Taim is so a Sithlord...er I mean Darkfriend
"Remember that old saying? Let the Lord of Chaos rule."