Commit 5821a2a implements a changed behavior in the case of failure to save settings.
The new behavior is that there are three "criticality" states for saving user data - "none", "important" and "critical". Most cases of saving data are set to "none". After using the configuration menu, "important" is set, and when exiting NeoLemmix, "critical" is set.
When the state is "none", if saving fails, NeoLemmix waits 50ms and tries again. If this too fails, NeoLemmix silently continues, but sets a flag so that the next save attempt will be (at least) handled as "important".
When the state is "important", NeoLemmix will make up to 5 attempts to save (again seperated by 50ms). Much like above, failure involves silent continuing, and the next save attempt will be handled as "critical" no matter what.
Only if the state is "critical", and 10 failed attempts occur, at this point an error message will be displayed. I'm considering also attempting to save the new configuration / save data to a new file in this case, which a user could then manually replace the actual ones with.