If it turns out that there’s a cheap, widely available, already-studied treatment that achieves something even close to the 100% cure rate observed in the paper, the timeline for total shutdown looks much shorter, no?

You don't think the markets would skyrocket if a real cure that is easily manufactured was discovered today? Sure, there's still a lot of pain to follow but the markets have priced in a lot of really bad scenarios where the virus kills large numbers and shutdowns last a long time.