That 20% drop brought its stock value back to where it was a year ago, which was an all-time high for it then. Investors that have held it for longer than a year can still sell it at a profit.
And to your point, investors could have sold for over 25% of profit as well if they had sold it earlier today. So I still stand by saying that this is huge change. Besides, this thread is not about long term, just invest in index funds so I just fail to see the point.