The problem with a lot of potential surviving states is there's no reason not to assume the age of nationalism would still arise. Burgundy and Byzantium might make it to the modern era, but they'd then probably be just as doomed as Austria-Hungary and the Ottoman Empire. Of course, Switzerland and Belgium survived, but the former carefully balanced local autonomy, while the latter has come close many times to being torn apart.
It's easy to see a historical accident allowing an area which today is a separate nationality to retain a separate state (Scotland, Brittany, Catalonia, Sardinia, etc.) It's much, much harder to imagine a new nationality arising in Europe without a POD before 1500. Savoy probably had the best shot - if they held on, they could have developed an artificial national standard which bridged the French and Italian dialects and made sure the nation kept a separate identity.