Even if you bought your rig on credit, you're still on the hook for making those payments regardless whether you have the machine off or on, so the cost of the machine is still a sunk cost.

Therefore, it'd make more sense to keep it running for so long as the machine hadn't been repossessed and the profits from mining outweigh variable costs such as electricity.

Repossession and liquidation can be a slow and costly process and the initial cost of the machine is also a sunk cost from the perspective of the lender and a mass wave of defaults could put their liquidity at risk. So, they have an incentive to make accommodations to the borrowers in order to ensure at least some payments keep flowing.