Chipotle shares have now dropped more than 25% since the record high set in mid-June.Shares of Chipotle Mexican Grill (CMG -8.35%) are taking it on the chin today. That's because its highly successful leader is leaving the company. But investors may just be panicking, and that's never a winning investment strategy.Chipotle shares plunged as much as 14% and were still trading more than 10% lower in midday trading after the company announced CEO Brian Niccol was leaving to become the new CEO of Starbucks.Nicc ...