Plot inconsistency with Helena dialogue

The city of Sarn rests atop a great rupture in the earth, overlooking the Phrecian Forest. The Emperor's Road winds around the side to bypass the cliff. The far side of the broken bridge is quite far from Sarn.

The ancient Vaal pyramid does burrow upwards in its entirety, meaning it no longer connects to the cave system below. The massive amount of earth displaced by the pyramid's ascent fell into the space below it.

However, this is not shown for gameplay reasons (so you can replay those levels with a friend, for example). Similarly, quest bosses will respawn in their respective areas even though they are canonically dead.