Is it an option for you to maintain a set of tests which simulate behavior on the tables?
I've have great success doing this with datawarehouses (i.e. star schema, large tables with few writes). You run the tests after each index change on acceptance. It caught a errors.
For OLTP it's harder, you need to record some production workload and reply it. At your scale it's easier said than done, though.
If the change that was introduced required creating a new index, it's unlikely that a test would have though to remove the now-outdated index or testing performance if the create-new/remove-old operations were reversed.
I've have great success doing this with datawarehouses (i.e. star schema, large tables with few writes). You run the tests after each index change on acceptance. It caught a errors.
For OLTP it's harder, you need to record some production workload and reply it. At your scale it's easier said than done, though.