She filled in for Kari Byron on Mythbusters when she was out on maternity leave.. I enjoyed watching her on the show.. Jessi Combs was a professional race car driver, and she passed at the age of 36 in a jet car crash. She was in the car attempting to break a land-speed record in the Alvord Desert in Oregon. Read the People.com article here. Terry Madden her boyfriend and a member of Jessi's race team posted this Wednesday..