The sustainability of public finances would hardly change, since a prolongation would do nothing to improve the other factors that determine the sustainability of the current debt level: growth prospects and the primary surplus.
Furthermore, a prolongation of Greek government bonds in an environment of prevailing strong doubts about the sustainability of public finances would make it impossible to accept them as collateral for refinancing operations under the existing rules of the Eurosystem’s collateral framework, and consequently large parts of the Greek financial sector would be cut off from funding.