So there apparently is a passage in the novel that states Theramore in every alternate reality was destroyed by the Mana Bomb, even the land being destroyed in realities where Theramore was never built.
“After reaching the crater where her tower once stood, she found the Mana-Bomb shattered with the Focusing Iris left within. The explosion was amplified by it, and the sky was lit with shimmering portals to other realities so that every universe, even where Theramore was never built, the land was decimated with the impact of the bomb.”