Life testament, illness and Buddhism

I would like to ask a question about ones *last will* and how buddhism views that. In Denmark where i live we have an option called a "life testament". In here there are 2 options that will be taken into account if one becomes severely ill or are about to die. 1. Does one want life-prolonging treatment if one is about to die? 2. Does one want life-prolonging treatment if illness or injury is leaving one behind without the possibility to take care of oneself either physically or mentally? I was wondering if im breaking any buddhist rules if i answer no to any of those? I have tried thinking about it but i cannot fully grasp it at the moment. Lets say i was in a traffic accident and was left as a vegetable. By writing the life testament and answering no to life-prolonging treatment because it would only op hold the life of a vegetable am i then breaking anything? Is this the desire/craving for non-existence im wandering into here? Should i just let things be and play out according to my kamma. Im a bit confused. Help would be much appreciated. Thank you. May you be happy, peaceful and free from physical and mental suffering. Harshani