"Dormant Membership"

Hans Werner Sinn and Friedrich Sell have a shining new idea for the eurozone: let the struggling eurozone countries freeze their membership, re-introduce their national currency, and return to the euro through ERM II. Exchange rate can then re-enter as a tool to restore competitiveness. They cite good historical examples, such as the time Germany decoupled the D-mark from its link to the dollar in October 1969 and later resetting it at a rate 9% lower or Argentina breaking its peg. MR=MC would question the legal aspects of putting a freeze on struggling Eurozone countries' membership to the euro though. How would bonds be re-denominated? At what rate?