a pretty reliable indicator, is if there's a hint, or a lot of blue to their appearance.... they've been overheated, and WILL be warped.
that's not to say they aren't if they're not blue, just that it's fairly common..... a few downhill emergency stops while moderately heavily laden , from the far side of 70 , can cook the discs , especially if the situation demands that you keep the brakes on when stopped.... the disk gets heated unevenly at that point due to continued stationary contact.....
the omega is better than some vehicles at resilience to that, but it is by no means immune
you should see how often i had to change front discs on my V6 Sintra. woefully undersized for the size and weight and power of the vehicle (heavier car, smaller rims, smaller discs than omega, but same 3.0 v6 engine, basically imagine a V6 7 seater miggy, with the effective driving position (height) of a range rover or transit van... )