The issue of unaffordability of universities if loans were drastically reduced would be a painful transition, but only a transition. Universities are unsustainable from a customer perspective as they are, and something needs to give.
A 4-year degree should also not be as widely required as it currently is, which is something else that needs to correct, which would happen with a collapse of graduates.
But as mentioned upthread, if we simply keep things as they are and throw good money after bad, people are going to have to be in school until they're 30 in order to meet the minimum requirements for mediocre jobs. Better to have some tough times to weather, given that you can always enroll later in life after things have settled, assuming it's something around a 5-year correction.