A fork this big (dozens of blocks covering multiple hours of transaction history) already happened in August 15, 2010, due to an unrelated bug: https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposu...
A fork this big (dozens of blocks covering multiple hours of transaction history) already happened in August 15, 2010, due to an unrelated bug: https://en.bitcoin.it/wiki/Common_Vulnerabilities_and_Exposu...