Carbohydrate depletion to the extreme can be very uncomfortable. It can be fatal if you lose control of your bike from disorientation due to low blood sugar. Your body will usually make you stop before that. You won't have a choice, because your body's choice of energy substrate, at this point, is fat--which takes longer to metabolize than the carbohydrate stored in your muscles and liver or the glucose in your blood.

A trip, if well planned, will include a nutrition/hydration/electrolyte aspect to the plan. If you know your needs and formulate a plan to meet those needs, then all you have to do is stick to the plan.