“As its sovereign-debt crisis nears a third year and rescue efforts fail to stop the rot in financial markets, economists from Pacific Investment Management Co.’s Mohamed El-Erian to Harvard’s Martin Feldstein say ensuring the euro’s existence may require members to leave the 17-nation currency region. The result would be what El-Erian, Pimco’s Newport Beach, California-based chief executive officer, calls a ‘smaller, much better integrated, fiscally strong euro zone.’”