If trouble strikes...
You have useful automatic rolling backups of navobj.xml, as described above.
Copy them somewhere safe before you run OpenCPN again, as they are automatically rolled over, and you lose the oldest one for each invocation of OpenCPN.
Rename the "best" one as navobj.xml, and the contents will be automatically used by OCPN.
The OpenCPN logfile also serves as a backup through the "LOGBOOK:" entries.
These can be used to reconstruct a GPX track. A windows utility for hat purpose ia available here:
https://github.com/nohal/LogBookExtractor/downloadsGood luck.