Now imagine something on a bit smaller scale that brought the end of the Ice Age 12,800 years ago. Here in North American it wiped out nearly all mega fauna.
My impression is that geologists and geo-physicists have pretty much given up on a space object impact in Canada around 13,000 years ago.
It's a fantastic theory - meteor strikes one mile thick glacial ice - but the supporting evidence is just really, really thin.
One small correction - the last major ice age began to end around 20,000 years ago. There was a significant North American cold spell (Younger Dryas) that began about 13,000 years ago.
Whether or not the cold spell had an impact on the mass extinction in North America, and whether a space object might have caused or ended the Younger Dryas, are definitely still being debated.