Do the trains all still run on the holiday? I'm thinking in particular the Artesia out of Rome to Paris leaving on the evening of the 15th. I can't find any place that lists dates the trains run or don't...
Both Trenitalia (www.trenialia.it) and Deutsche Bahn (www.bahn.de) websites show a direct (no changes) night train from Rome to Paris on August 15. It leaves Roma Termini at 18:36 and arrives Paris Bercy station at 09:10. Both websites have English versions. If using Trenitalia website, you must use the Italian names (Roma Termini and Parigi Bercy) even when using the English version.