Sorry a couple trillion dollars in deliquent debt changes hands every year.
Shakaru should do what has the highest ROI%.
It may be to repay all investors in full.
It may be to walk away from everything.
It may be to settle for a fraction of the amount owed.
Fungibility of money is an irrelevant aspect of the conversation, it's not money that is at
stake here but rather reputation and credibility (credit history to put it in a jargon yanks
can grok).
That is a short sighted view. Any decision can be traced back to NPV. Not paying the debt has a cost but paying the debt also has a cost. Free markets work when each side is aggressively working in the own self interest. That is why settlement on debt is often an option.
Many debts would simply never be repaid if settlement wasn't an option. Given the choice of paying in full or accepting a temporary hit on ones credit many would just take the hit rather than trying to pay down an impossible amount of debt. The ability to settle provides a net benefit to both sides.
