The pilot's failure to follow proper IFR procedures by not adhering to the published missed approach procedures, which resulted in an in-flight collision with tree-covered terrain. Factors contributing to the accident were a low ceiling, fog, rain, and the insufficient operating standards of company management by allowing unauthorized single pilot instrument flight operations. Additional factors were the pilot's impairment from cocaine, alcohol, and over the counter cold medication, and the FAA's inadequate medical certification of the pilot and follow-up of his known substance abuse problems.