Of course this also assumes that unsealing Lorkhan would destroy the world, which is arguably false. Lorkhan is connected to Nirn as a physical place. Thus the taunt of his heart "But when Trinimac and Auriel tried to destroy the Heart of Lorkhan it laughed at them. It said, "This Heart is the heart of the world, for one was made to satisfy the other.""
Lorkhan is dead and or mantled by Talos.
Not sealed.