A convergence can only occur one of two ways, I imagine: If there was some natural law of the fictional Zelda universe which makes it possible, or if there was some divine influence. I think we can rule it out as a natural law in the fabric of space-time – nothing in-game establishes that the timelines should combine after being split. That only leaves divine influence.
In theory, the Triforce, with it's ability to grant any wish, could be used to converge the timelines. This is practically impossible, however. Someone would first have to come to a realization that there are diverging timelines tracing back to the nexus event of Ocarina of Time. I don't think there is a way such a discovery could be made.
But what if it could?
There is only one satisfactory way I could even imagine this working narratively. The Child Timeline has no significant decline of Hyrule it seems, and the Hero of Time actually proves he was from a different timeline. If this was recorded, perhaps he even left behind a memoir or something, and someone discovered these documents, that would be a good way to write an explanation for them using the Triforce to merge the timelines. Why they would be compelled to use the Triforce to do this is beyond me, but I'm sure someone could write something interesting with this premise.
Any other narrative set up would make no sense, because it would be impossible for documents to survive the Great Flood, and the Downfall Timeline is the result of the concept of Multiple Histories, meaning there would be no tangible way to even prove to anyone that they are on a divergent timeline because it's a timeline that was created naturally, not by tampering with time.
The cop out way to shoehorn a convergence would be to pin it on the gods. One day they just decided to merge everything. I think the premise I set up is more interesting.
For the record, I don't think BotW is the result of a convergence.
In theory, the Triforce, with it's ability to grant any wish, could be used to converge the timelines. This is practically impossible, however. Someone would first have to come to a realization that there are diverging timelines tracing back to the nexus event of Ocarina of Time. I don't think there is a way such a discovery could be made.
But what if it could?
There is only one satisfactory way I could even imagine this working narratively. The Child Timeline has no significant decline of Hyrule it seems, and the Hero of Time actually proves he was from a different timeline. If this was recorded, perhaps he even left behind a memoir or something, and someone discovered these documents, that would be a good way to write an explanation for them using the Triforce to merge the timelines. Why they would be compelled to use the Triforce to do this is beyond me, but I'm sure someone could write something interesting with this premise.
Any other narrative set up would make no sense, because it would be impossible for documents to survive the Great Flood, and the Downfall Timeline is the result of the concept of Multiple Histories, meaning there would be no tangible way to even prove to anyone that they are on a divergent timeline because it's a timeline that was created naturally, not by tampering with time.
The cop out way to shoehorn a convergence would be to pin it on the gods. One day they just decided to merge everything. I think the premise I set up is more interesting.
For the record, I don't think BotW is the result of a convergence.