In a recent shoot on a Red One, I put the lav audio on mono track 1, and a boom mic on mono track 2. After importing it into Premiere Pro and placing my clips into a sequence, I felt the boom mic track 2 sounded too echo-y, so I deleted it from the sequence timeline and proceeded to editing my video using track 1 audio only. Well, now the client wants to use the boom mic track.
Is there an way easy way to restore the the 2nd audio track while keeping my edits in place?
Well, it's not really easy or automatic, but if you park the playhead at the first frame of a clip in a sequence, target the track, and then hit M to match frame, you'll load up the master clip for that clip instance into the Source Monitor. From there, you can edit the whole clip or just the audio portion back into the sequence; it should be already marked with an in and out point to match the duration of the sequence clip.
After doing the necessary work form Colin's suggestion, a tip for future edits is to never delete unwanted audio. Mute the track instead. It's much easier to unmute a track than to restore clips.