If the insurance/accident investigation assessors do their jobs properly, they will crawl over every car that has been involved in an accident with a very fine tooth comb and find those 'modded' vehicles and refuse to pay out the owner for any damages to their vehicles. Harsh, yes, but the only way to start enforcing the law properly.
What they do is smash the dpf out of the exhaust pipe and then refit it. The loss adjuster may never know it's been removed.