I think we know the control board was bad. The fridge kept running when set to "OFF."
Phil's suggestion that the evaporator fan motor may have burned out after its blades were immobilized by accumulated ice certainly sounds plausible to me.
It seems to me that even if the fridge was running for a few days non-stop, that would not be long enough for a large glacier to form on the evaporator and cause its fan to seize up. That points me to the defrost timer. I think if the defrost timer is dependent on the control board, it wouldn't have necessarily needed to be replaced. If the defrost timer operates autonomously, I would consider it the prime suspect for causing solid ice to accumulate on the evaporator and wreck the evaporator fan.
It sounds like both the control board and defrost timer went bad, perhaps either of them failing because the other one did, and the evaporator fan was collateral damage.
Regardless, none of this forgives the tech for not de-icing the evaporator so the refrigerator could be used immediately afteward.