I went to the building and could not get through the forcefield yet... but the window above it was accessible with my hooks so I climbed up there and ran the entire area. Now that it is open to go through I can not and have not yet been able to get him so spawn to move the quest along and unlock the next area.
Many players have done the same thing and its not just this boss either. If you rest within the same realm, the boss will respawn.