It is only a matter of time untill something like that happens. It happened to us twice. Once in Vienna, and the last time in Rome. We were on vacanza, so it was not the end of the world, but it involved extra costs. In Rome we had to stay an extra three days ( so hard to take). The airline had a bogus reason but never went into details.
As we were in the airport to leave my wife found a notice in the airport regarding the rights of passengers in the EU. Click the link below to bring you to this page.
Much has been written on this subject, but if your are delayed or have your flight canceled check this site. Also check it if your baggage is lost or delayed. Last year Air Berlin would not let us bring our suitcase as carry on even though our connection was only an hour. Our baggage did not make it.
We went back to the airline (Eurofly USA div of Meridiana) through our credit card company and saved almost $1000. They did not contest our chargeback through the credit card company.
With all our trips to Italy, still like Alitalia the best.
The site below may be of help also:
May the help be with you!