The most exquisite swan song-type songs ever written, IMO, are Richard Strauss's Vier letzte
Lieder, especially #3, "Beim Schlafengehen" - -
and #4, "Im Abendrot" - - though for your
"seasons" theme, you might want to use #1 of the cycle, "Fruehling (Spring)" -

Also: "Ich bin der Welt abhanden gekommen" -
- from Mahler's Rueckert-Lieder

Also: "Absence" from Berlioz's Les Nuits d'ete -

Also: "Me, me, and none but me" - - from John
Dowland's First Booke of Songs