"face the music" from "face the music of war"

[Jonathon Green]

Two other proposed etymologies:

1872 Schele De Vere _Americanisms_  601: _Face the music, to_, a slang
phrase, derived, according to J. F. Cooper, from the stage, and used by
actors in the green-room, when they are nervously preparing to go on the
boards and literally face the music. Another explanation traces it back to
militia musters, where every man is expected to appear fully equipped and
armed, when in rank and file, _facing the music_.