There are two immediately implausible things about this storyline: 1) that a slacker would amass a large amount of I.O.U.s (after all, by definition he doesn't do much of significance for anyone, including himself) and 2) that childhood I.O.U.s, which are usually incurred for small favors like help with homework, setting someone up on a date (again, things that slackers wouldn't normally do) would be significant enough to be convertible into cash, and the large amounts of cash which would be necessary to save the family home. And why should these 'childhood debtors' feel at all indebted to this person after such a long time?
Here's what I would do to make it more plausible: instead of reaching out to near-strangers to collect childhood I.O.U.s, I would have the protagonist reach out to estranged family members, trying to convince them to help him/her save the house. There would be ample scope for old wounds to be reopened, reconciliation and/or further estrangement, and lots of other good human drama (and perhaps comedy as well).
Oh, a movie that has a similar concept is the recent Thai martial arts movie
Chocolate: the heroine is an autistic girl who has the ability to learn complex martial arts simply by watching Tony Jaa Thai boxing movies. When her mother, who used to be a gangster, falls ill with cancer, the heroine goes to her mother's debtors to collect on her loans. In this situation the plot is (slightly) more plausible, because a gangster with some influence would be expected to incur substantial monetary loans to various shady people.