You wrote in italian but I’m replying in english because it can be useful for others.
My suggestion is to write all the metadata in the sidecar files. So even if the case that you lose you db, you can rebuild it from the info contained in the xmp files.
On Digikam:
These are my settings in Metadata > Behaviour
These are my settings in Metadata > Sidecars
Tip: at the bottom of the Captions tab on the right, there is a More dropdown. If you select images, you have the option to read/write the tags in the sidecar files.
I strongly suggest to TRY on a sample folder, it before but this is what I will do. HAve a backup…just in case 
Example of workflow:
Let’s say you have everything in Linux. You change the settings above and write all the metadata in the sidecar files.
You switch on Windows, plug the drive, sync the folder at read the data from the XMP file. Now you db contains all the data from the file.
If you write the data in the XMP you will be always able to build the db from scratch.
Hope it helps.