I doubt it'd slip through the cracks... The late fines are fully automated. The advertised price is a daily rental rate. For every day you have the item, you get charged that amount. Once you hit the maximum amount, it stops charging you and you can keep it (at that point, you've paid the full price of a new movie or game, but just own a second-hand one...)

It could potentially work out like netflix letting users keep the discs they had.