Sebastian Hayward is one of the Hayward brothers that are being attacked by Forsaken Castaways. He and his brothers plan to escape Hayward Fishery[37, 84.6] by boat, but they are in need of repairs before they can flee Gilneas.
It's unknown what happens to the brothers after the evacuation.
It's possible he might be related to Deathstalker Hayward.
Patch 4.0.3a (2010-11-23): Added.