Like you and Graeber said: debt is not a feature of capitalism, it is at least 5000 years old. Debt crises are nothing new and there are exactly two ways to get out of them: a) the debtors stop repaying, and the creditors forgive the debts, b) the debtors stop repaying and hang up the creditors. This is no threat to capitalism, only to some capitalists.

In my view there is the unemployment crisis underlying the current debt crisis. A degree of productivity that allows traditional full time jobs only for a small minority. I don't see how capitalism could cope with it.