a debt that has been agreed to is not onerous by definition
the usual procedure is a negotiation of a settlement that cancels the debt, usually involving liquidation of assets and a tax out of your income, that usually won't fully satisfy the loan but it is all that is reasonable
bondage through debt is not permissible, though in Islam it is permissible for an enemy to serve you as a slave as compensation for their aggression previously for some period of time rather than be killed
and yes, the size of the finance industry has to shrink under a hard money system, because it is very high risk
defaulting on a debt you signed up for is a sin though, that's why it does have to be properly amended
