We all know Dagoth Ur died/disappeared during the ending of Morrowind when the Nerevarine destroyed the enchantments on the Heart. Only the physical body of the Heart of Lorkhan was destroyed, the heart itself still exist in some way or form. Since Dagoth Ur was linked/fused to the Heart unlike the Tribunals who only drew powers from it, i think theres a chance he might still be alive in some way or form just like the Heart of Lorkhan. Maybe hes in spirit form or something like that.

In Dragonborn we get to meet Ash Spawns, molten flaming zombies that are scattered in and around morrowind when red mountain mysteriously erupted. I think these ash spawns are creations of Dagoth Ur since ash creatures are usually related to him like ash priest, ash slave, ash ampires, ash storms etc. Or these ash spawns could be the angry spirits of the Sixth House members but i still think Dagoth Ur is involved in some way.

My life for the dark god Dagoth Ur!!!!! show the sissy Alduin and Miraak how real badasses do things!