well imagine if the db change involves a merge of 2 columns, if you wanted to roll back the changes, how would you determine how to seperate the data. For example, address line 1 and address line 2 has been merge to 21 dave street, london, london, uk. How would you know before the merge, what address line 1 contains and what address line 2 contained. Restoring a DB backup is a massive change and i'm guessing they only have 1 DB and it's massive, and can't afford to have 2 db of the same size, it'll prob be petabyte size, it requires bringing it down, however fixing forward a DB change can be done on the fly without outage. In previous roll strat i've wrote, it's been to fix forward if possible, timebox it to 1 hr, if it can't be done then get the backups, turn the whole thing off and restore.