Of course there are opups on QF -- all airlines do this, though a few (e.g. SQ) have a policy of no op-ups to F and will pay for a downgrade instead. Internationally the chances for opups on QF to F and J is slim to none as on some routes J and F sell out sooner than Y ... so there simply are no empty J or F seats to upgrade to. When some are available, they are snapped up by paid upgrades, further reducing the chance for an opup. Even WP status is usually not enough to get an opup, so as Bronze your chances are zero -- there will be a hundred pax with higher status ahead of you to get an opup. This status problem would also apply on QF domestic routes; I doubt a Bronze has ever gotten an opup except as compensation for some other problem.
As for what does QF do when Y is oversold and J/F are full? They reroute (with varying levels of convenience and compensation). Again not unique to QF, but QF pays a lot less compensation than AA or UA for example.