There probably would have been a few that survived in areas far from the boloid impact where conditions might not have been or become too severe. However, I think that loss of the ozone layer may have been worldwide.
Maybe the effects of the impact (if there was one) weren’t as bad as first thought. (smaller , less penetration, more absorbed by the ocean)
Who knows? We learn or think we learn some new info around every corner we look. Tomorrow could be something totally different.