Sadly, quite nothing to do, see:
22 pages term paper replaced with pound signs.
The file seems indeed empty. Perhaps acknak will manage to recover something with Emacs, I've not yet re-installed it on my system.
Any special event like power shortage?
Note that AOO 4.0.1 may be less prone to such failure.
Check the temporary folder of the system (see in OOo Tools>Options>OOo>Paths). If there are folders like sgmlf.tmp with a file having the same name inside, make a copy of that file, rename it in .ods and cross your fingers. If you have not rebooted, you might have those files still there.
LibreOffice 25.2 on Linux Mint Debian Edition (LMDE Faye) and 24.8 portable on Windows 11.