Apparently, Brandon said the chapters aren't in order and he implied he may have left out a few.

Not in order makes "Lighter than a Feather" perhaps far more ominous than if it was early in the book.

If Lan is to fall, it would make sense it happens at the end of "act 2" when TG really begins, after an heroic attempt to contain the invasion which begins in the prologue, apparently. A fitting end for him would be to die destroying Isam or attempting to (and personally, I would have Moiraine die at his side too. I still hope Moiraine is mostly a plot device to bring Mat back to the TOG, that she won't have a major role in the LB, or at least not for very long).

A problem with Lan surviving to the end is that he seems to steal Perrin's thunder a bit. They share Isam as a foe, they both had their families slaughtered by evil anf their lands overun by the Shadow (Malkier fell, the TR has pushed it back), both have a Borderland nation and its crown awaiting them - and could be the the main leader of the Borderlands at least through TG, and things really seem geared for Perrin and the wolves to become a major opponent of shadowspawn down the line once Perrin has assembled his wolf army - which I think happen in KOD (the wolves can hardly take on Forsaken and Dreadlords in TG... that's a job for Mat with channellers at his orders, or for Rand, Logain and co. Trollocs, stuff from the Blight however...).

So perhaps Lighter than a feather could be our chapter 50...