People want to live and die on their own terms. We all wish to have control on our lives. When we think of death, it is the dying which is what most worry about . Of special concern is when we lose the capacity to make decisions and with time lose the capacity to understand what is going on as happens with Alzheimer's and other dementia of multiple causes.
This is a chronic illness of slow decline with an average life span of about 7 to 10 years. Some of course may last less and some more years. Initially the loss of function and understanding is mild , perhaps forgetting names and places. But it progresses to inability to drive, then to simple tasks, losing ones way , becoming very forgetful and eventually not recognizing family, difficulty in eating, swallowing, walking and becoming totally dependent on others.
Concern most patients have is that they do not wish to live with help of artificial means beyond the level they feel worthwhile.
Again, if families do not know their wishes then they are left with the uncompromising situation of making hard decisions. Thus it behooves us all to let our loved ones know of our wishes and what may be important to us in case we get dementia.
You may consider a wording similar to what I am suggesting here below to be added to your advance directives as your wishes in case of dementia:
"If my mental abilities have declined to a point whereby I am unable to communicate rationally ( or none at all), unable to recognize my loved ones, unable to swallow food or water safely ( or none at all), unable to care for myself AND it is unlikely that my condition will improve, then I wish all life prolonging treatments to be stopped (medicines, machines, pacemakers, artificial food and water etc.) and nature be allowed to take it's course.
BUT please continue any treatments necessary for my comfort so that I may not suffer."
This is obviously a very severe end stage dementia but you may wish to change the function level to any other as you wish.
Once you have it in writing or have at least talked with your family and physician about it, you have taken appropriate steps to control your destiny as well as possible.