Mental Capacity Act

I have been discussing 'the rules for death' with an emphasis on those patients who wish to die at home. In particular, I wish to understand whether operational district nurses believe that a family carer who is at home with a patient who arrests (only the carer and patient present) is 'obliged' by the Mental Capacity Act to make a best interests decision, about whether to phone someone, or to allow the patient to die in peace if the family carer knows the patient wished for that to happen.
Preferably, with the 'source of your answer' as well. At the moment, I am interested in the 'legal' answer (ie, assume the family carer is not panicked, and retains some composure).
I am quite interested, in whether operational DNs will usually have read the Mental Capacity Act itself, not read the Act but read the Code, or read neither and have only read more tertiary/local guidance which contains an interpretation of the Act ?
I only joined this site about an hour ago - I see 'attach files' which is interesting (I have written this stuff up extensively as PDFs - but I am very interested, to understand what other people would write about it !).