When MAF disconnected, ECU default values are used instead of real reading from the MAF. At this time you could have increased RPM's and/or other parameters changed so ECU is not complaining. If you drive the car and it starts misfiring at random times (after20,30,50min), it could be that needs to run for specific period of time in certain RPM range. For that reason it's best to test the car while there is no load (or almost no load) in parked position. Test it on idle speed and see if it starts misfiring and repeat the measure if it does.
If not try raising RPM's to 2k for couple of minutes and see if that's going to do it or fix it.
Let us know