On WEDNESDAY Oct 17, which was the 2nd episode of Nashville, SF was playing St. Louis baseball. Therefore a fall in attendance on Live TV was expected. As I recall, the 3rd episode held even with the 2nd. Also as I recall Nashville was the winner in that time slot for all three episodes. But I could be wrong. But if it was the winner, I don't think ABC would dump it mid-season.
The fall back for LGF could be selling Nashville to a cable TV channel.