I hope Bethesda proves everyone wrong and it is a permanent effect.
I don't understand why people are so sure it won't be permanent. Whiterun still has wreckage around the tree, Helgen is still in ruins, and if we want to go further back, just think of Kvatch.
If we're going off to other games that Bethesda has produced, just remember Megaton in fallout 3. You could permanently blow it up and pollute the entire surrounding area with radiation and an eerie green mist.