Disclaimer: The characters aren't mine, nor am I profiting from this.
Notes: In my head, John was listening to the Presto from the 3rd Movement of 'Summer' in Vivaldi's The Four Seasons.
Sherlock left his music. It's still there on the stand, his latest—last—composition, scrawled messily in his sprawling, manic hand. John can still hear the notes coalescing, slow and elegiac and oddly fierce, like a Viking ship going down.
Sleep is a minefield that John avoids, studded with memories of blood on pavement and hitched breaths into mobile phones. Staring at the ceiling isn't much better, so John goes downstairs and turns Sherlock's stereo on. Sherlock is not dead; Sherlock could come back at any moment and raise an eyebrow at John's being in his room, listening to violin music. The piece upshifts into something quick and feverish—Vivaldi, John thinks—and if he closes his eyes, he can see Sherlock playing it. He's standing in front of the window, his back to John, and the setting sun lights him up like a funeral pyre. His bow flies over the strings, fluid strokes that make the instrument sing, and his whole body surrenders to the music, consumptive and shaking—his inchoate curls and his incendiary white phosphorus heart.
It's so beautiful that John could cry. He doesn't.
Sherlock left his music, and he could come back at any moment. So John lies down on the floor, and waits, and drowns in the sound.
John waits for a very long time.