The end of life for a CF patient is peaceful. Morphine or other strong narcotics will be administered to relieve any pain / feelings of breathlessness. Anti-anxiety meds, such as benzodiazepines, are administered if the person is obviously distraught. It's not fun... it's death. But it's also not that bad. I know this because I experienced it myself. I nearly died last year from pneumonia and a collapsed lung, was on a ventilator for weeks, etc. I accepted that I was going to die, and would sit there thinking "any moment now..."
Some of you may think "but you weren't in end-stage CF"... which is true. But, end stage CF or not, I was in full respiratory failure for a prolonged period, and only by luck (god, thought power, WHATEVER) did I manage to recover. I even caught some glimpses of "the other side" during this experience.
It sucks... but it's not that bad. If the person has family by their side 24/7, it makes things so much better. I didn't have people with me there 24/7, and I remember all I wanted was to see my mom. I now understand why men who are shot on a battlefield and dying call out for their mothers. For young men, mothers represent love, protection, healing... the womb.
So, in summation, don't dwell on it. It's not that bad.