The Flash Season 2 finale shocked us all in the final moments, when Barry undid two years of plot (not to mention character development) in order to run back in time and save his mother's life. As Barry's decision plunges Season 3 — and all the other DC shows — into an uncertain new timeline, we're left wondering what this means for Barry's immediate future. Will he run back to the present? If so, what will he find?
When it comes to time travel, it's difficult to work out the rules of the game, especially when the writers keep moving the goalposts. Barry running through time used to be simple — as soon as he arrived at his destination, Barry would merge with his past or future self, as we saw in the Season 1 episodes "Out Of Time" and "Rogue Time". Then, everything changed in Season 2.
Instead of just a fragment of a previous timeline, time remnants became much bigger players in Season 2. The episode "Flashback" saw Barry go back in time and replace his younger self, while in the finale Barry used his time remnant as a sacrifice to stop Zoom's doomsday device. This means we've now got two separate theories of what happens when a speedster time travels, making for two possibilities for Season 3: Either the Barry we know will merge with his alternate timeline self, or he will become the time remnant.
Option One: De-Powered Flash
Merging with his alternate timeline self seems to be most likely, as this is what happens in the comic Flashpoint. In the comic, Barry wakes up to find a world changed in the wake of his time travel, and crucially — he has no powers.
Still remembering the previous timeline, Barry has to find out exactly what happened and why everything is different. This could be an interesting situation in Season 3, as Barry has to play catch-up, living a life he's not familiar with. We can only assume that this altered timeline is similar to the one the Reverse Flash ran back from in Season 1, wherein Harrison Wells doesn't create the particle accelerator until years later.
The idea of Barry having no powers is intriguing, as we have to wonder whether Barry will try to replicate the particle accelerator explosion in order to regain his identity as the Flash. There is one problem for this storyline though — we've already seen it happen.
Several episodes in Season 2 dealt with Barry losing, then regaining his powers. It was definitely an interesting plot thread, but it might seem repetitious if we see the same thing happen again in Season 3. Luckily, there is another option.
Option Two: Double Trouble
So, back to time remnants. This is an idea which is... tenuously logical, to say the least. We haven't had a full breakdown from any character in the show on exactly what time remnants are, and why sometimes time travel means Barry encounters remnants rather than merging with his past self.
Without delving into the psuedo-science of this (because we'd probably fall into a plot hole), let's just run with the possibility that Barry might find himself a man out of time in the altered present. This would definitely be something we haven't seen before, as Barry is forced to avoid his other self, dealing with the fact that he's the sole survivor of a doomed timeline.
Interestingly, this way our Barry might actually still be the Flash. With the altered timeline Barry not having powers, our still-powered Barry could take up his heroic identity, saving the citizens of Central City from fiends — and maybe investigating other heroes who sprung up in his stead. If Barry does become a time remnant of the previous timeline, this could persuade him that his decision was a mistake, leading to him changing time again in an attempt to reset the timeline to how it used to be.
From a storytelling perspective, that might be a good idea for the show, as this could simplify matters for the fans (not to mention having interesting consequences for the multiverse).
And then there's sneaky option three: Barry remains in the past. After all, when Eobard Thawne changed the timeline in Season 1, he immediately lost his powers and was forced to stay in the past, rewriting history so he could get home. Again though, this might be a bit repetitive. Ultimately, the options for Season 3 really are endless, and it's anyone's guess what might be in store for Barry.