Too many seem to have been cheating for so long they are unaware of which way is up and which way is down.
An aircraft must LAND AIRWORTHY with regards known defects and scheduled maintenance. Landing 6 hours after an MEL item has expired means the aircraft flew in a known unairworthy condition. Just as departing for a 6 hour flight knowing the next c check is 2 hours away is too.
That was the origin of the maintenance statement and you may not depart on a sector unless there is sufficient time remaining.
The MEL process is to enable continued operation with unscheduled defects. The preamble also makes it clear that the defects should still be dealt with asap regardless of any given time frames. Trying to justify that an aircraft is ok to fly when an MEL item expires during flight highlights there are still too many gangsters in the business.
There should be processes in place to ensure this doesn't happen should there be a lack of spares or particularly difficult troubleshooting. Overruns are also possible.
Departing knowing an item expires in flight is not an available option.