habitats move during ice ages, they don't disappear and reappear
Ice ages aren't like asteroid collisions, they take a thousand years or more to get going. That's time for species at the southern end of their range to move further south, or move downhill on a mountain range. When the glaciers retreat, the process is reversed.
And the glaciers usually don't scrape down to bedrock, they probably add more high quality pulverized soil than they take away.
In 2005 I helped biologists at Glacier National Park measure plant density in a wildflower field that twenty years earlier had been under a glacier.