Kill the trash mobs as your leisure. When you're ready, go up the ramp from the central chamber and engage Izinar Malkevantrii. Afterwards, take care of A'Lyn D'Morte, even though it isn't aggressive. Upon it's death, the breakable wall to the southwest becomes interactable. Destroy it and the coffin behind it to spawn the final boss V'Rin D'Morte.