Both Mary and Emma are correct ... using the Moodle UI's, no.
From command line and a text editor with a great deal of re-editing the xml flies of an un-archived backup of the 2.7 on could acquire some parts but not all. Example: in a 2.x backup, the 'roadmap' for restoring the course contained in a moodle_backup.xml file. A valid 1.9 backup had a similar file called moodle.xml. Now changing the name won't do the trick by itself. One also has to edit the xml file to make it compatible with the 1.9 restore process. For the files contained in the 2.7 course - files.xml and the related 'files' directory for the actual files themselves (by contenthash name - not humanly re-cognizable by filename.ext).
One could NOT get users for sure ... too much has changed in the area of passwords.
It might, however, be possible to get the files that were uploaded to a 2.7 extracted from the backup in 2.7 format, out into an 'extracted' directory by their humanly recognizable file names/types with some work (command line only).
The real question is ... just how important is it to do this ... 2.7 course backwards to a 1.9 ... and how much time one really wants to spend on it.
'spirit of sharing', Ken