Peaceful but sad non-vocal music?

Try something by Explosions in the Sky.

Mogwai?

I’ve always enjoyed the theme to Cast Away in this regard. (There are clear parallels, too, between the scene you describe and the idea behind the movie, too.)

The Memory of Trees by the Taliesen Orchestra. It’s a re-working of an Enya song.

Massenet’s Meditation from Thais seems perfect for what you want.

Memories
Mahalo
Greensleeves
Black Heroes
Moonlight Sonata
Flute Fruit
Erbarme dich
De-a dreptul superba
Violin Concerto in A Minor BWV1041 – Mov. 2–3/3
June Barcarolle

John Frusciante – Murderers

Samuel Barber’s Adagio for Strings

Loss of a Twin. Perfect, beautiful, sounds like something from a movie.
I Don’t Want to Become a Vampire. Don’t underestimate it because of the name, or be put off by the vampire-crazed comments on YouTube! I’ve never seen The Vampire Diaries and yet this music is so beautiful and inspiring.
And of course, Any Other Name, from American Beauty. The music made me want to see the movie.

^ These three stand out most in my mind. They’re all very beautiful pieces of music.

NIN – Ghosts I

Many songs by Yanni would fit.

Try the soundtrack to “Last Exit to Brooklyn” by Mark Knopler. It’s pretty dark and moody so much so I listened to it maybe 3 times to try to like it. It is definitely one of those things that a person needs to be in the mood for. It’s been out for about 12 or 13 years.

http://en.wikipedia.org/wiki/Last_Exit_to_Brooklyn_%28album%29

here ya go http://www.youtube.com/watch?v=C0Z3d2VjAWM

Oops. That Ghosts 1 link had really poor audio quality. Here is a better link.

Would you mind something classical?
This is peaceful but has definite notes of melancholy.
There’s also a violin version from an album called “Sweet Sorrow”