If I was in severe pain and absolutely no chance of recovery to a somewhat normal life I would talk to my family, get my affairs in order, and then commit suicide. I believe I would still go to heaven and my family would be relieved from seeing me suffer to an inevitable end.
But the ones left behind are not relieved. I wasn't relieved when my mother ended her life. As a matter of fact, 4 years later, and I'm still pissed at her. We needed her around to help us through the loss of our father, who was knocking on death's door with cancer.
Maybe that's kinda selfish, but losing them both at the same time (10 days spart from each other) was a terrible blow to my family.
Suicide is NEVER the answer.