"Which currencies are included in the U.S. Dollar Index?
The U.S. Dollar Index contains six component currencies: the euro, Japanese yen,
British pound, Canadian dollar, Swedish krona and Swiss franc.
Before the creation of the euro, the original USDX contained ten currenciesâthe
ones that are currently included (but not the euro), plus the West German mark,
the French franc, the Italian lira, the Dutch guilder, and the Belgium franc.
The euro replaced the last five of these currencies."
https://www.theice.com/publicdocs/futures_us/ICE_Dollar_Index_FAQ.pdf
not so much if any individual country or countries dropped out of the euro, but if
the euro ceased to exist, which would cause massive problems and is unlikely
to occur. I think that once 'they've' got all the indebted countries 'under control'
in the sense of austerity measures, Italy, Spain, Portugal, Belgium are the main
ones, then they might allow the ECB to act and feed in some funds - print money.
they won't allow that at present since Greece etc haven't yet taken responsibilty
to 'Do Something' besides asking for handouts - good money after bad