What also is interesting is if the dagger is destroyed in 2019, and the dagger is what held Thawne in place in 2049, then how long was Thawne in prison and how would have have been kept there in the first place, unless they used other meta dampening tech?
Presumably, you would think that since the ability to capture Thawne does exist in 2019, his capture in 2040something didn't require the dagger and they would have some other means to control him.
But it sure looks like they will destroy the dagger in 2019, it will disappear in 2049, and Thawne will escape.
I'm really hoping that somehow, all of this leads to the Tornado Twins' existence. Imagine this scenario--the dagger is destroyed, which leads to a series of events that prevents Nora's birth. However, Nora still exists as a time remnant, no different than how Thawne still exists despite Eddie killing himself.
In the new timeline, Nora is never born, but her parents and everyone still remember her because she is a time remnant. She can even remain on the show. It might even be a cool cliffhanger to have either Bart Allen or the Tornado Twins appear and Nora be like "WTF?"
Either way, I really hope next season they break it into two arcs instead of one. One villain for a whole year is repetitive and requires too much filler.