“Hello Earth” by Kate Bush.
A worship song as I’ll be going up to see Jesus.
My absolute impulse knee-jerk response: I’ll Remember by Madonna. It’s my song for my Aunt who was my loving shepard through most of my childhood, it focuses on gratitude and maturity, and I think it would end things on a positive note.
Iron Maiden, “Hallowed be thy Name”. Especially if I were to die by hanging. 
My inner snark would demand that it be I Fought the Law, and the Law Won.
Huh. I’m surprised it took l this long for The Great Gig in the Sky.
I might want to substitute “The Ash Grove” for “Be Thou My Vision,” since it’s my favorite song of all time.
Beethoven’s Ode to Joy.
If I’m on death row then Gangsta’s Paradise would sound appropriate. Play it loud for all my homies on the block as I walk the green mile.
See, now I was just going to go with “The Song that Never Ends,” but I like the way you think.
Has Vogon poetry ever been set to music?
Of course the most appropriate song for a hanging, “25 Minutes To Go”. Sadly, the song only lasts for 3:30 minutes…
Good choice, but I’d pick (from the Carol Burnett Show):
Bolding mine. What’s your definition of ‘song’ here? Apparently no singing is required. Could my ‘song’ be an entire symphony by Beethoven or Mahler? Obviously a ‘song’ that is both long and very very good is the ideal combination.
Always Look On the Bright Side of Life.
I was thinking of songs as they are colloquially known. A song from your past maybe. But since folks are torturing the definition, I won’t deny your submission.
But myself, I think trying to name a long song just to stretch it out is missing an opportunity.
That’s why I asked about instrumentals, because to me, “songs as they are colloquially known” are sung by someone, so you seemed to have a broader definition of ‘song’ than mine, and I wasn’t sure how broad yours was, and what its bounds were.
Even with the inclusion of instrumentals, I wouldn’t include an entire symphony, because the music stops in between movements. The second movement of Beethoven’s Seventh is a different piece of music than the first movement. But to me, neither one would be a song. ETA: As I see it, a song can have an instrumental section, e.g. the long version of “Light My Fire,” but singing has to be an essential element.
Can I go with John Cage’s As Slow as Possible? (the Halberstadt remix of course)
Having said all this, I’m going to go with Roxy Music’s “More Than This.” For some reason, the melody just captures for me the feeling of peacefully and joyously drifting from this world to the next.