Save your audio changes in Sb as an ASND document. From the Help Files for both CS4 and CS5:
Adobe Sound (.asnd)
ASND format lets you readjust fades and effects, and store history snapshots that restore previous edits. This format also supports multitrack mixes, which let you combine multiple audio files and scores. Adobe Flash, Premiere Pro, and After Effects import ASND files, tightly integrating those applications with Soundbooth.
If Edit in Soundbooth works like Edit in Audition does, the first thing that happens is that a PCM/WAV file is written, and will replace the Instance of your Audio on the Timeline (very important part), and this means that your original Audio stream, say from a muxed AV file, is still in your Project Panel. When the Edit in Audition is done, that replacement Incident is updated in the Timeline. Nothing is done to the original Audio stream, and one can easily delete that replacement WAV with the original Audio stream and then just start over.
Jeff's method looks like the easiest way to do things, as you do not need to go through the process of Deletion and replacement, so would be my workflow, but you should still have your original Audio stream, sitting in the Project Panel, without any SB, or Audition changes to it.
Good luck, and if Edit in SB differs for Edit in Audition, I hope that someone one will correct me.