That rule must has changed then because in that scenario, provided the departure airport isn't a crew base, it is just a reduction of passengers, not seats. It is an exceptional circumstance.
"Exceptional circumstance" can be misinterpreted.
The occasion I refered to we operated Y148 B737's and our standard crew was 4 CC, operate flights around Europe and N. Africa with minimum crew then an operator is asking for trouble and in the event of a sickness down route I wouldn't interpret that as exceptional ... that someone got sick!
On the day in question that I refer to we'd had 2 CC go sick, one before departing base and one down route and when we subsequently read the rules there was nothing in them regarding "exceptional circumstances".