It will happen soon. In fact I expect it to go down in the Path of Daggers book. Min sees him wearing a crown, he will rule. Egwene sees "a dark haired young man" (logain or Taim--though if Taim is Demandred, a theory to which i myself subscribe, it will be Logain after he kills Taim) drawing Callandor. She also sees him stepping over the paper dead Rand. So Rand is going to disappear, presumed Dead, and Logain will take over for a while. What he's going to do, is beyond me. Rand, on the other hand, will become a beggar. Remember Min's viewing of a beggar's staff and such? Rand has to go through the beggar stage and mix with the people and get humbled. Gotta go through the beggar stage before you can truly become a great king. It's in the rules. As to how he will come back, i expect that Cadsuane will take Alanna in hand and the two of them will hunt his butt down along with a few maidens and some wise ones. He will be back to being the Dragon Reborn by the end of the book though, just in time for the last battle and his Arthurian boatride, which will occur in book nine.