There's no cause for panic.Shares of burrito chain Chipotle (CMG -9.54%) tumbled as much as 14% Tuesday morning after CEO Brian Niccol stunned the industry by announcing his departure to take the top job at Starbucks (SBUX 20.16%).That sell-off wiped roughly $10 billion from Chipotle's market value, showing how respected Niccol is after turning the business around from its E. coli scandal and guiding the stock to monster returns. Starbucks, meanwhile, rocketed 21% higher on the news, adding $20 billion in m ...