Hmmm ... now that would be a tough project. So many people to think of. I might have to pick one I've already written, if I had one with enough genuine warmth and hope worthy of sharing with all of my friends and family. I think Embrace, which I sent you last month, might be the best candidate so far. I did play one of my songs at a friend's funeral once. Very surreal experience. It wasn't about death, or about him in any way, just a song he had always really liked. He passed really suddenly though, I think you remember the time? And when I and his mutual friends were planning the service, they asked me to play a song for him, and that was the only one I had any reason to pick. You know it well, I think? Personally, picking from others' tunes, I could probably go a bunch of different ways, but njósnavélin by Sigur Rós would be today's pick.
Yes, I do recall that time and I do know that song well -it's beautiful. It would be interesting to write a song, knowing it was your "last letter" to friends and family and humanity in general. -a tough challenge