There's nothing you can do except contact your insurance company, assuming the ring is insured along with your other possessions.
While it's possible housekeeping or maintenance saw it and pocketed it, it's equally possible it went down a drain. got bundled with sheets and towels bound for a commercial laundry, or was sucked into a vacuum cleaner. For this reason, accusing hotel staff of theft won't get you anywhere.
It wouldn't hurt to write a letter--not an email, phone call, but a physical letter--explaining why the ring can never be replaced and asking them to look again. Lay on any sentimental value it has with a heavy hand. Offer a reward in Euros for the person who finds it. If it did get stolen, such a letter might get a thief to "find" it.
It's too late now, but the lesson here is that you don't travel with your best or irreplaceable jewelry.