Yeah, this sure sounds familiar (am a veteran of the CO bonanza). I'd say that CO did readjustments in maybe 30% of cases. If US is determined to do the same then it may well cost it MORE to untangle the mess than to leave the miles intact and carry them, since the miles aren't valued that highly as a liability, anyway. Not to mention the ruffled feathers or PR problems anytime you take something away like that.

Of course a lot of this depends on how big the bonanza was and for how many people. If the CO experience is any guide, the number of fliers and miles will be tiny compared to the overall base. IMO they should program the changes but leave existing miles in place.

(Full disclosure: I'm a Dividend Miles member but haven't flown US since 1991. Have been using 11-year-old miles to get magazine subscriptions)