My parents have made their wishes known to all us kids. My wife and I are very clear about each others wishes. I can't imagine having to decide whether to use extraordinary measures to keep a loved one alive or not at that intense emotional moment. Even then, it would feel like your insides were being ripped out.
Please 'Have the Talk'. Be clear about whether or when extraordinary life saving measures should or should not be used. To seal the deal, get a Living Will documented. Unfortunately, each one of us will have to make that decision at some time. Start a dialogue today...