Why is everyone here so sure that the original timeline still exists? Some producer or scriptwriter saying something in some interview on some website doesn't mean anything. Perhaps if he said it in a DVD audio commentary or in one of the DVD special features, it would carry more weight, but the only thing that will prove the two-timelines theory correct, is to see the original timeline, after the destruction of Romulus and disappearance of Spock and Nero.
Why does it have to be proven? None of this is real. It's all fiction. Even if the original timeline had been "erased" within the Abrams films' continuity, there'd be nothing to preclude us from continuing to tell fictional stories set in the original continuity -- just as it's possible to carry on telling
Spider-Man or
Batman stories set in their respective comics continuities alongside their ongoing movie series. Whether you believe they're coexisting timelines within a single reality or merely two distinct creative interpretations of a fictional franchise, there's absolutely no reason why the existence of the new timeline should make it impossible to continue writing stories set in the old timeline. It's all equally unreal anyway.
And there is precedent within the literature. You mention
The Chimes of Midnight, showing how the "Yesteryear" timeline unfolded in the era of the TOS movies. Whether you choose to interpret it as an alternate timeline that "actually" still exists or merely a hypothetical "what if it had continued?" tale, it's still just as valid as a work of fiction.
And then there are Diane Duane's later Rihannsu novels. Even though her earlier novels were contradicted by various things in later Trek, she was still allowed to continue the series with tales that were explicitly out of continuity.
Besides, the "history being overwritten" model of time travel is just plain wrong. It's bad science and it doesn't make any logical sense. If there are two different versions of a given moment in time, it's nonsensical to see it as one "replacing" the other, because a single moment in time can't come before or after
itself. That's just silly. By definition, two different versions of a single moment in time exist simultaneously, parallel to each other. The only possible way to have two different versions of a single span of time is if they exist in parallel timelines.
The only remotely plausible way to justify the fictional trope of a timeline being replaced by a different one at the moment of time travel is if the two histories coexist from the moment of their creation onward, and then merge back into a single timeline once history catches up with the moment the characters went back in time. Like one road branching into two that run parallel for a time until merging back into one. So even the "overwriting" model involved parallel timelines, at least during the interval in between the time travellers' arrival in the past and their departure from the future. All that's necessary for the timelines to continue to coexist is for that merger to be averted somehow. And you can easily justify that with a simple handwave, since it's all made up anyway.
So asking for "proof" that the old timeline continues is missing the point. We don't need proof. We can make up whatever explanation allows us to justify continuing to tell the stories that our audience wants us to tell. It's fiction, so the science exists to serve the story needs, not the other way around. Hell, the whole idea of a timeline being erased by time travel is a total lie, a fantasy that makes no scientific or logical sense but is made up to serve the dramatic needs of a story. So what's wrong with using actual
good science to serve our storytelling needs this time?