It’s not complicated. It’s just unthinkable.
1) Let the banks go under if they’re bankrupt. Make their private owners take the losses.
2) Refloat the banks, this will cost a TON less than having governments pay of private losses.
3) For countries with “unsustainable” debts after doing this, roll the debts over into 100 year bonds at 1% interest. If the bondholders don’t like that, that’s just too bad. No, they won’t “strike”, neither Iceland nor Argentina have any trouble getting loans.
There are other things which should be done, but that’s the basics. This is not complicated. It just requires being willing to stick the bill for the financial crisis with the people who caused it, financial elites.