What should ultimately be done with the public debt in the euro zone?

By the end of 2020, the public debt ratio in the euro-zone countries is expected to increase by 17 percentage points of GDP to 103% of GDP. What should ultimately be done with this very high public debt in the euro zone? Cancel the part of the government bonds held by the ECB (by the European System of Central Banks), which would bring the public debt ratio down to 72% of GDP by the end of 2020? Certainly not: this would be a default on these government bonds, which would trigger panic in financial markets. Put all these government bonds back on the financial markets, with the ECB selling the share of the bonds that it holds? Very probably not, given the risk of a debt crisis that such a sale would entail, especially for the peripheral countries. Permanently keep the government bonds purchased by the ECB on its balance sheet and roll it over at maturity, which is equivalent to cancelling this part of the debt. Keep long-term interest rates below potential growth in the euro zone for the remaining government bonds held by investors other than the ECB, in order to gradually extinguish this debt. The last solution is the most likely, even if it leads to a permanent expansionary bias in monetary policy.