If loan repayment is not made, or the collateral falls in value sufficiently that the loan becomes undercollateralized, the collateral will be sold to cover the outstanding debt. The outstanding debt can be invested on a new business, stocks or gold - its not restricted to buying digital assets.
Or do I have that all wrong? I really am not sure that I grok how this works, at all. I'm trying to figure out what is going on in this space and you seem to know a lot more about it than I do. I couldn't figure out another good reason to use an overcollateralized loan but it's clearly something people are interested in and using as a selling point for DeFi.
What actually happens if the borrower defaults on the loan? Do they "just" lose their collateral, or can they be held to account for the DAI somehow too?