As we've seen in the last episode, Barry runs through time, back to the night her mother got killed by Eobard aka Reverse-Flash. The original plan was to save her, but once he's there, his future self tells him to not save her. If you have some knowledge of the Flash, you'll know about the Flashpoint Paradox : a storyline in which Barry manages to save her mother, but everything else turns to chaos (Superman lands in Metrolpolis instead of Kansas, Batman is Bruce's father and he's a killer ... etc).
It's pretty easy to imagine that the Flash from the future already saved her mother in his past, that's why he tells Barry from the show to let her die, else disaster falls. Barry, of course, trusts himself and lets her mother die and that leads to the most emotional scene of the whole season
Then, after he runs back through time and lands the most spectacular punch I've ever seen in the show,
the wormhole does not close, because in RF's plan, Barry was meant to go back in time, save his mother and never return, but because he didn't save her, the timeline remained the same, thus the wormhole still exists. Ronnie and Caitlin manage to close the wormhole just in time. Barry and Eobard start fighting, and eventually RF gets the upper hand, as always. Then.... the moment we never expected (but we kind of did because it's logical when you think about it) Eddie shoots himself and dies, thus erasing Eobard from existence.
Now, this is where things get tricky. The singularity reopens, "why ?", you may ask ?
Let's backtrack a few episodes. As we all saw in episode 17 - Tricksters, Eobard goes back in time to kill Barry's mother, but in so doing, looses his ability to harvest the speed force. So, he takes the identity of Dr. Wells in order to speed up the particle accelerator project, and to create the Flash sooner (the Flash from Eobard's timeline is created around 2020).
Eobard had such a hand in altering this timeline, it's just logical that when he disappears from reality, it becomes too unstable. According to general time-travel laws (if there is such a thing) Harrison Wells and Tess Morgan are still alive, Barry's mother is still alive too (because if Eobard never lived he couldn't have killed Nora) and last but not least, the Flash shouldn't yet exist. That's why the wormhole reopens, it's the universe's way of fixing itself.
Well, I said why it reopens, now where does it lead. The following will be a lot of speculation based on what I've seen throughout the season, I may be completely off-course though and most likely none of this will happen or even be mentioned.
As Martin Stein says
A wormhole takes place, opening a gateway to time itself
Wormhole aka the Speed Force, yes I said it. I strongly think that a wormhole and the Speed Force are one and the same. As you can probably remember, Barry already traveled back in time this season, in episode 15 - Out of Time, to be precise. He didn't need a wormhole to travel back in time, right ? Sure, in the finale, the wormhole is there for Eobard because he can't harvest the speed force anymore. If he could harvest it, there wouldn't be any need for the wormhole.
So, basically the black hole leads to time and space, but it's more than just spacetime, it's also other dimensions/realities. We can clearly see a certain helmet belonging to Jay Garrick, the Flash from Earth Two (Barry is the Flash from Earth One), spilling out of the wormhole. This only means that the black hole is a portal to other dimensions, and not only time and space.
There's also another clue that hints at the multiverse in episode 10 - Revenge of the Rogues. It's hard to miss, and you need to be paying a lot of attention to your screen when it happens. Iris has moved on with Eddie, but she comes back to Joe's house to grab a few things and return Barry his red backpack. We can see what looks like a Batman comic.
That's it, when Barry runs upward the wormhole, my guess is, he's going to end up in a different dimension. As I said before, maybe I'm completely off-course and none of this will happen or ever be mentioned, but The Flash is coming back for a second season, so who knows what's gonna happen. When time-travel and dimensions are involved anything can happen.
See you all on October, speedsters !