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 10billionfromChipotle′smarketvalue,showinghowrespectedNiccolisafterturningthebusinessaroundfromitsE.coliscandalandguidingthestocktomonsterreturns.Starbucks,meanwhile,rocketed2120 billion in m ...