I think bison could survive. It'll be thousands of years between the population explosion of bison (which though the extinction of the American horse was a cause of it, it was also because of the extinction of the various Pleistocene bison species like B. latifrons and B. antiquus) and the domestication of horses. Bison numbers, though not as high OTL since they'll still have the American horse as a competitor, will be quite high. It'll take a while to put a significant dent in them, and hopefully after the first few population crashes (both of bison and people), the culture would adapt so the horse nomads don't kill off their most important prey. They'll have thousands of years to learn how to do this, compared to a few centuries while constantly being pushed on all sides by Europeans.
Depends which North American horse gets domesticated as to the range. That's certainly true with the Eurasian horse, but is it necessarily with the North American horse?
Depends which North American horse gets domesticated as to the range. That's certainly true with the Eurasian horse, but is it necessarily with the North American horse?