Odd Language #211: Left or Left?

‘Vergerin’s smile was grim. “They had the choice of signing new contracts with me—for I will not honor the old ones—or leaving. Not many left.”‘—Dragonseye, Anne McCaffrey, p. 363

The issue: “Not many left.” could mean that not many chose the alternative of leaving (which is the intended interpretation), but it could also mean that there are not many left (which would mean that many took the option of leaving).