They say it outright in 09Actually I didn't think it was clear from watching the movies.^ Yeah, I thought that was clear, too.
It was never stated that a new universe was created and the old one still existed.
I accept that it did happen as my TOS DVDs and blu-rays still exist.TNG is still shown on TV. They're still selling Prime Trek merchandise. No need to panic.
ST09 said:KIRK: There won't be a next engagement. By the time we've gathered, it'll be too late. But you say he's from the future, knows what's going to happen, then the logical thing is to be unpredictable.
SPOCK: You are assuming that Nero knows how events are predicted to unfold. To the contrary, Nero's very presence has altered the flow of history, beginning with the attack on the USS Kelvin, culminating in the events of today, thereby creating an entire new chain of incidents that cannot be anticipated by either party.
UHURA: An alternate reality?
SPOCK: Precisely. Whatever our lives might have been, if the time continuum was disrupted, our destinies have changed.
There's really no way the characters can know or say the Prime Universe is still there, but the Many Worlds Interpretation says it is ( as do the writers/producers).
I still don't think those lines were clear enough. I think many people needed the reassurance that this was not like a Guardian of Forever thing.
But what does it matter anyway as you point out the writers, producers, comics, CBS are all agreeing that the Prime Universe still exists. Even if they didn't we all know that the next interpretation of Star Trek could involve either universe.