Mostly just like everybody else: quietly and gratefully, or serenely, or screaming and whimpering.  What is unusual about them, as a group, "is not how much treatment they get compared with most Americans, but how little" (Arthur Giron).

This WSJ article discusses the reasons for that.  Mostly it's because they understand what's going on.

A contrary opinion is memorably, laceratingly, expressed in Dylan Thomas's "Do Not Go Gentle Into That Good Night."

When I was in radiology residency, I got an unexpected call from aunt Dorothy – Dottie – perhaps my favorite of the eight aunts.  She had had polycythemia rubra vera for many years, managed by regular withdrawals of the red blood cells that were multiplying ad lib.  The effect of that excess would be to raise the viscosity of the blood and promote stasis and clotting.  That is what eventually happened, clotting all the veins in her liver and causing liver failure, ascites (fluid in the abdomen), and edema.  Liver failure allows ammonia to accumulate in the body and affect the brain, leading to dementia, coma, and death.  It was treated at that time by oral administration of lactulose, a non-absorbable polysaccharide that binds ammonia in the gut to some extent, and promotes rapid evacuation of intestinal contents.  It reliably produces constant flatulence and episodic frequent diarrhea.  But it did control blood ammonia levels.

Dottie found this intolerable.  She was a quite proper, though not prim, Bostonian, and this was no longer amusing.  She called to say I had to do something, since her husband and her son were adamant that she had to stay in hospital and suffer this regime.  They were in despair and unable to care for her at home.  True enough.

I flew to Boston over the weekend and went directly to the hospital.  She was in bed, bright and alert, with the same piercing blue eyes, and she was glad to see me.  I had reviewed her chart, and told her that I too thought it was best that she stay in hospital.  I went to the window and, my back to her, described the lovely autumn day and the colors of the leaves.  "Jim," I heard her say, "it's not going to work.  You have to get me out of here or I'll go walking down the street with my johnny flapping."

I turned.  Her belly was huge, and her limbs were spindly, but she looked serious.  She said she had cared for Bumpa (father-in-law) at home until he died, and by all that was holy, she was going to die at home and not in this place.  I said it would be very hard on the husband and son.  No, it won't, she said.  I'll stop taking this medicine.

My recollection of what followed is hazy, but I think a hospital bed was put in the sun room on the ground floor, and she died a couple of days later with her family present.  As she might have phrased it, she was a peach.