I thought the idea is that touching the dark one with the OP is what tainted it. Rand knows this, and he will find a way to avoid touching the dark one with OP while sealing the dark one to such a state that it is eventually forgotten. I suggest this will require the shadar logoth power--Moridin's "old enemy, old friend"

My best guess is that he will use the unbuffered callandor with the two most powerful women available (Alivia and Nynaeve) to channel all of the true power into the shadar logoth ruby. It is totally possible the dagger will be lodged in his side at the time, and he will burn himself to ashes in the process.... hence..... blood and bloody ashes. I'm only half joking.