gdb = r'Database Connections\MyDBConnection.sde'
arcpy.env.workspace = gdb
featclsInDatasets = []
for fds in arcpy.ListDatasets('','feature') + ['']:
for fc in arcpy.ListFeatureClasses('*_OLD','',fds):
featclsInDatasets.append(os.path.join(fds, fc))
#list the featclasses in datasets
for fc in featclsInDatasets:
print fc
#list the featClasses not in datasets
for fcmain in arcpy.ListFeatureClasses('*_OLD'):
print fcmain