Yes, if you did not leave the mines, as far as I know it shouldn't cause any problem to use the Luculla Forest data from the start of the mine with the save at the end.
As long as the mirror is fixed upon leaving the temple area, rather than with the collapse of the mines and them getting filled with lava, that is (though you have Leandra's spell IIRC, so there is not much reason to return). I'm not sure if there are any other events in the mines that affect Luculla Forest. It is moderately easy to check, though, and you can revert to the earlier save if there are any issues.
The save file format can be decompressed by the EE pak extractor
After starting the ConverterApp.exe program, switch to the 'PAK / LSV Tools' tab, in the 'Extract Package' section, for the 'Package path' browse to the save's lsv file, then for the 'Destination path' browse to that or another profile's savegames_patch folder and enter a new folder for the extracted files (you can copy/paste the path from the path listed above and edit it; ie to be '..\savegames_patch\SaveName-extracted') and click the 'Extract Package' button.
After you do this for the save at the beginning and end of the mine/temple area, rename or delete the lucullaforest.lsf file from the levelcache folder in the extracted QuickSave_3 folder, then copy that file from the earlier save. You should be able to start the game and load the extracted QS3 save, then exit without the error, and hopefully without other issues (ie if there are any changes due to quest progression). The game will see the extracted folder as a save, so you don't need to worry about packing it.