Did Earth already go successfully interstellar before warp was invented? We have references to failed missions: the Charybdis might or might not have been built for sublight interstellar stuff, but ended going to another star by wholly different means, while NOMAD was supposed to be interstellar in 2002 (?) already but got rear-ended by Tan Ru at an unknown point of its mission. Khan went off the deep end without anybody noticing. Etc.I think somebody on Earth would have put together enough resources to send at least an unmanned Warp 2 probe to explore Alpha Centauri
Quite possibly, crewed exploration vessels might have been on their way to nearby stars before, during and after WWIII. Some might have reached their goals but, lacking subspace technology, would not be able to inform Earth until well after Cochrane's flight. No Tellarite or Andorian intercepted Khan; possibly other Earth "coasters" might reach their targets unaccosted, too, and even make first contact with some neighboring cultures.
Well, we have "In a Mirror, Darkly".Would Earth have united so quickly? Would it have abandoned currency-based economics? Maybe Earth would have been a much more aggressive, expansionist world.
Although that supposedly takes place in the Mirror Universe, where everybody already is evil, lesbian and (when applicable) goateed, not in some sort of a "regular" alternate timeline where the parameters are otherwise identical to ours.
Timo Saloniemi