If you did want to do a "digital mixdown" (which is the same as merging audio regions with the glue tool) and keep the original regions:

First create a new identical track (Ctrl-Return when the track is selected) and then just make an Option-drag {PC?] copy of those regions you wish to merge. This way you will retain both the original regions and the newly copied "digital mixdown" files/regions. Note that Logic does not delete the original audio files when merging regions to create a new one, so going to the previous version of the song will load with it's original files/regions. So always be saving and keep a backup folder of at least 10 songs.