Then you should have pressed “Yes” to Save Changes or backed up to WAV export first. 
If you only recorded four hours at 44100 Hz you should only have 4800 AU files. Are you recording at 192000 Hz or similar?
Are you sure there is no autosave file?
Are you sure you have the naming sequence correct? How exactly did you sort by time then rename the AU files?
Assuming you have the sorting and naming correct you could try Append Import: Append Import . However this has limitations because it imports files in memory. You should not import more than 1 GB or 2 GB of AU files at once. More importantly, the way you sorted the files may not agree with the order in which Append Import imports them. See Append Import - #32 by steve .
Gale