What would happen if tomorrow all private and public debt was erased?
It would depend a lot on how the debt was "erased." If you are simply suggesting a transfer payment from creditor to debtor, what would force such an event? Or would it be voluntary? If it were forced, then you would have a threat to private property rights and therefore, a disincentive for further lending. Security of capital would be diminished and all investment might stop overnight.

This question is very broad. But the answer of what might happen would depend very much on the details of how all this might come about.