You wanted to know if anyone other than the doctor's practice would find out if you were dismissed?
I know that the contract that my PM doctor uses says that they have the right to trade information with your pharmacy, other doctors ( which means your GP, and any doctors you might request that they forward your records to), so the answer to your question would be yes, they would all know. I've been there when they have called other doctors involved with a patient that they have dismissed for not taking their meds or having a dirty screen. And it says clearly in that contract that if you are dismissed, they will only forward your records to another doctor, they will not release them to you.
If your contract has that release about information on it, or something similar then those things could happen to you too.
If you are taking one less a day, that might not be a big deal, but if you are prescribed 6 a day and you are only taking one, then your best option might be to tell your doctor that you don't need so much medication since you are trying to cut back or feeling better than you were.
If they do serum levels or quantatative tests, then they will show what your blood plasma levels are, and if you are below the threshold, then you might be in trouble and accused of diverting if you can not produce the correct amount of meds......
Urine tests don't do quantatative amounts but have a minimal amount that they will detect, and if you fall below that, you will show a negative screen.....which will lead to being dismissed from most PM offices.
Anyway, it may be different at your doctors, so read the contract and if you are not taking a good amount less than you are prescribed a day, you might want to consider asking him to cut back on the amount he is prescribing, rather than take a chance at having a negative urine screen. Or have a discussion with your doctor and tell him that you are taking less meds most days and ask him how he wants to handle it. Either way, it's not worth loosing pain management over if you really need it not to do something the right way.