RJ was just shocked the fact the mass suicide of a whole people and their children left so many readers totally indifferent and that just because we didn't know the Amayar much at all, many readers just didn't care for what they did, or felt no sympathy for the Sea Folk.

It seems to me that the Amayar's main role was to that the Cleansing of saidin was balanced out by something really horrific. This makes me wonder how the Pattern could balance out Rand's success at healing the Bore...

I doubt the Amayar will have a much larger role than this. They're all dead...

As for the Sea Folk, at this point if they aren't fighting the Seanchan before the Seanchan stop or halt their conquest - and this battle looks less and less likely to happen (their prophecies say the Seanchan will be repelled more than once, however), it's hard to see what they'll do in the Last Battle, except the obvious possibility that when things gets really bad on the mainland (we're close to that) Rand asks them to evacuate as many refugees (children, women, elderly) as possible to their Islands for the duration of the LB. Obviously, he may also ask the Windfinders to stop standing aside and join the fight too. He's already asked Harine to stop sending their male channellers to their death.