Another option... keep your final Master (and alternates) in the project, and be able to A/B or null test it against the live mix:
- Create a track called Master Bounce.
- Set its output directly to Main Outs on your interface (i.e. parallel with the Master Bus), and invert the phase.
- Select nothing (Ctrl+Shift+A), and Bounce to Tracks with source = Buses and only the Master bus selected, and your Master Bounce track as the target.
With the inverted Master Bounce track playing in parallel with the Master bus, you can check for nulling of the two signals (may not null to silence, depending on FX and instrument plugins used, but should be close).
Or you can mute the Master Bounce track, and group it's mute button in opposition with the Master bus mute so you can A/B the two tracks (with or without disabling the phase invert on the Master Bounce track - doesn't much matter)
As an aside, I also like to create a "Pre-Master" bus that has no mastering FX on it, with peaks kept below -6dB, and a "To Main Outs" bus after the Master that I can use as a target for the Master Bounce track, and the Metronome bus to get control of the summed output level to A/D converters.
You can bounce additional, alternate Master mixes to new lanes in the Master Bounce track, and use exclusive lane soloing to isolate and A/B them.
When you've got what you want, Export just the Master Bounce track with Source = Tracks.
Or you can export the un-mastered "Pre-Master' bus to send on to a mastering engineer.