There are many Theories on the Last Battle on this Forum, yet here is one I feel is very solid in its foundation and has a sense of RJ's poetic irony.

During book 12 Rand announced to Moridin that he was going to "Kill the Dark One." Something that Moridin considered monumentally stupid to say. However, Rand may eventually come to realize that he has come into contact with the Dark One's own Being once before, and has successfully annihilated it. This occured during Winter's Heart and it brought to mind several key points.

During Winter's Heart, Rand Cleanses the Taint from Saidin using a giant funnel of Saidar over the course of hours to pour every drop of Saidin into Shadar Logoth. The taint which is often referred to as "the Dark One's Backlash" when the Bore was closed was annihilated as was Shadar Logoth. Keep this thread in mind as I weave a complex web to explain The Last Battle.

During Book 12 we find that during one of his Lucid moments Lews Therin comes out and says the way the patch on the Dark One's prison was made was "We Touched Saidin to Him". This can be used to directly correlate the taint on Saidin with the Dark Ones Own essence.

Enter, Padan Fain. Unassuming in book one, Fain becomes far more as the series progresses. He is "Distilled" at Shayol Ghul in an incredibly painful process that makes him instantly hate the shadow almost as much as he fears it. He then becomes one with Mordeth in Shayol Ghul during the chase after Rand and the others. Finally, he finds a "kinship" with Machin Shin in the Ways.

Padan Fain has accumulated three kinds of evil within him, but the most important thing we learn about him is that in his singleminded venture to destroy Rand, the only thing he hates with nearly the same fervor is the Shadow. This can be connected back to Shadar Logoth and Mordeth.

The evil in Shadar Logoth started as a hatred of the Shadow. The people hated the shadow so much, and the fear and doubt grew so much, that the people turned on themselves in fear and hatred. This fear and hatred was so powerful that it lived beyond the deaths of the inhabitants of the city, becoming Mordeth.

Rand is able to cleanse the Source by pitting the evil of the Dark One's taint against the evil of Shadar Logoth, in which they annihilate one another. I feel that the same will happen at Shayol Ghul come the Last Battle; Rand is not planning it this time, but Padan Fain and the Dark One are going to Destroy one another.

The proof that they are on equal power footing can be found with the two unhealing wounds in Rands Body. The only thing that kept Rand alive was turning those wounds against one another so they could fight each other instead of destroying his body. This ties in well with Robert Jordan's love for mixing in other Mythology and High Fantasy within his novels.

One Quote that can be found on the praise page of nearly every WoT book is the phrase "Robert Jordan has come to Dominate the world that Tolkein Revealed." I find this significant considering that the way that The Lord of the Rings ended was with a seemingly side character tying up the final plot. I would like to point out that Gollum was definitely Insane, and was definitely Evil. However, his evil was different from that of Sauron, and in the end he served the greater good inadvertently. I would like to point out a parallel between Moirane and Gandalf in that both advise sparing the lives of the nasty little evil character very very early in the series. Moirane claims that No man is so far gone to the shadow that he cannot return to the light. (I am paraphrasing) and I see a fitting end tying up with these characters. One last connection before I try to paint a picture of the end of the Dark One, and that is Rand and Moridin's Bond.

Rand knows the Karetheon Cycle speaks of "Red on Black, the Dragon's Blood stains the Rocks of Shayol Ghul." We also see that Moridin's livery colors, as well as the colors of his fortification in the Blight are, in fact, red and black. Min has a viewing of Rand and another man coming together, and merging, and only one man surviving. Since we know that Rand is connected through his Balefire intertwining with Moridin, and Rand acknowledges that Lews Therin had never been there in book twelve; we can safely assume it is Rand and Moridin who will be fighting for survival.

Another Prophecy that Rand is trying to deal with is the answer he received from the Redstone Doorframe where the snakes told him "To live, you must die." put it all together and this is what I think will happen:

At Shayol Ghul there will be a cataclysmic battle between Rand, the Dark One, and Moridin. During this time, I cannot speculate what Mat and Perrin will be doing, but I think that Mordeth Fain will show up again. I think that the key to Rand's surviving the Last Battle will be in him and Moridin finally connecting and his own consciousness winning out over Moridins, while his own body is destroyed by Padan Fain. I feel the Seanchan woman Alivia may aid in this in some way that I am open to suggestion to,as I am not sure how. The Dark One and Fain will be forced to fight one another in some form be it incidental proximity or just Fain deciding to finish off two foes in the same day now that he has killed Rand's body. In the end, just as the taint on Saidin and Shadar Logoth were BOTH annihilated, so too do I believe the Dark One and Mordeth Fain will die.

This would allow Rand a fully healthy body for after the Last Battle has ended, with no unhealing wounds, and both hands. It would allow for his blood to be spilled on the rocks at Shayol Ghul. Also, it would allow the world to perceive that the Dragon has died and the world can go on living happily. Rand and his trio of wives could exist peacefully with however many kids he would want, and while the new body would take some getting used to, it would be a definite improvement over death.