The Kingdom of Etruria could survive... After all, it was nothing more than an upgrade of the Grand Duchy of Tuscany only with different rulers. Restored Haspburgs in Tuscany could ask to keep the title King of Etruria.
Just out of curiosity, the Grand Duchy of Tuscany that Elisa Bonaparte ruled and the kingdom of Etruria ruled by the Bourbons was for all intents and purposes the same state with the same borders. Yet Napoleon never made his sister a queen, Hell, he never even allowed her the same ruling powers as he and his brothers. He told her when she countermanded an order to arrest the Queen of England (Luise of Stolberg), that she had no right to do so (as her brothers did), merely to appeal to Paris. Did that have something to do with a misogynistic streak in his nature?
In the case of Italy, it was ruled by Napoleon in name and the viceroy was his stepson, Eugene de Beauharnais. Eugene was also Napoleon's heir for the Kingdom of Italy unless he had a second son. Eugene was popular among the allies I believe and he got along very well with his Bavarian stepfamily, but he was far too loyal to Napoleon so I don't think the Allies would consider him keeping the throne. No that a unified peninsula has better chances of surviving: Italy was nothing more than a concept to Metternich (if I remember one of his quotes right).
Eugene de Beauharnais was understandably loyal to Napoleon
until his first abdication. Thereafter, during the Hundred Days, his Bavarian in-laws (pushed by the allies) made him swear
not to help Napoleon, at the risk of forfeiting anything he had gained out of the deal (principality of Eichstatt, duchy of Leuchtenberg). He was also designated the successor to the Grand Duchy of Frankfurt during the Empire, so perhaps the Congress could reason that that would be suitable recompensation for him. I mean, the king of France was at first willing to recompensate Hortense with the dukedom of St-Leu (she lost it in the 100 Days), why couldn't Eugene remain as Grand Duke of Frankfurt?
Also, the Grand Duchy of Berg was (theoretically) in the hands of the prince royal of Holland, Louis II Bonaparte. What would be cool is if the Netherlands picks up Berg at the Congress, and uses it as a sort of secundogeniture for the prince of Orange, or that it goes to another branch of the house of Nassau (don't know which ones were still drifting around).
The Grand Duchies of Salzburg and Würzburg were simply the restyled territories of the previous archbishoprics. They were originally created for the deposed Grand Duke of Tuscany. So maybe a Tuscan prince or a personal union with Tuscany for one of them. There were more than enough Hapsburg archdukes floating around in 1815.
As to the Grand Duchy of Warsaw, it was kept as the so-called Congress Kingdom of Poland. It was ruled in personal union by the Russian emperor. It could be united with the duchy of Danzig and given to...well, IDK who would be a good candidate.