Bob's Winery has been negotiating with Wine Depot Ltd. to sell 40 cases of wine being held in the warehouse at Bob's Winery. Right after signing the final document it was discovered that, unbeknownst to either company, a fire caused by a lightning strike had destroyed the warehouse four days prior to the contract being signed.

Does Bob's have to deliver the 40 cases of wine? What is the main legal concept that supports your answer?