The deal is:
1) Existing damane remain enslaved.
2) No more hunting damane outside Seanchan lands.
3) Seanchan emissaries can spread the Gospel of the Collar throughout Randland.
Because she has no moral objection to slavery and no moral objection to leashing rabid dogs. She believes channelers are rabid dogs. Rabid dogs that destroy enemy troops with great effect.
My interpretation of Brandon's statement about the Epilogue is that he made extremely minor changes to the epilogue but it was otherwise RJ who wrote every scene of it.
Since almost nobody meaningful dies, the answer almost has to be Gawyn by default.
That would also be my answer, as in "Writing Gawyn's death in AMOL was very hard; I wanted my first contribution to the WoT saga in The Gathering Storm to be Gawyn's death so nobody had to hear from him again."