Will all European countries revert to their original currencies when the euro fails? ?

The USD had been the strongest currency in earths history so they will likely peg it against the USD. 

The Yuan, like the Euro before, is showing promise, but it is inflationary & the Chinese peg it to help promote their cheap exports, something completely different from what most European economies need. 

Due to USD history and US-Euro relations, they would likely go through a dollarization, pegging their currency to the USD. 

Another possibility is a neo-Euro, a new Euro currency, with likely a slightly different name, which would be used by Germany and other more stable European economies which want to maintain a Eurozone currency.

Economically,if the Eurorization is failed, the next step should be the dollarization, or even the Yuanization. A small local currency could not survive anymore.

If the euro fails, it is possible that several nationstates fall apart as well.

There are small-scale experiments with local/provincial complementary currencies already

No.

Rather: they will probably revert to the nomenclature of their most recent pre-Euro currency.

Of course, the possibility also exists that they will form another multinational currency.