If that happened then probably investors with weak hands will sell their Bitcoin because of fear. But still, many investors too will take advantage that price to buy more Bitcoin because its an opportunity for people who missed to accumulate before the price reach an ATH before.

Anyway, I believe its not going to happen for the price to return back to $8k value (though there's a possibility). Because currently the standing of Bitcoin is different from before, adoption is already happening and users are growing. Hence if the price will move below $20k, its expected that many investors will buy back, and majority of those people are aware of the history of Bitcoin.