Quote Originally Posted by Vyrerus View Post
There is, and it's the 8UC short story they put up that established that an alternate timeline still exists where their own time machine had no effect on their own timeline (meaning their own time machine cannot interact with their own timeline). But I get it. It's a deeply convoluted mess, and you've spent a lot of time thinking about and seeing it a certain way.
The short story only establishes that the other future still exists, not that it has split apart all the way back to the dawn of time. It only needs to split as far back as whatever key event defined the beginning of a change that ensured the Calamity could not occur.

We have no proof that the earliest effects of the time travel did or did not take place in the history of the other timeline. They don't know the state of the First, they only work out later that it was the rejoined shard and that they need to go there, so the tower could have appeared in the history of their timeline and the Exarch's plan simply failed, resulting in a stable time loop from their perspective – not that they would know about it, as all sign of the attempt would be wiped out along with the First itself.