So what would have happened if there was an accident on, say, Nov 9, involving one of the carriers suffering a magazine explosion that blew the ships to pieces and the blast/debris causes one of the now remaining 5 to be a total constructive loss and/or another to be damaged enough to require weeks to repair?
Would they have gone with a depleted strike force of 3 or 4 carriers?
Three decks no chance. That means to complete two strike waves (which was the minimum expected to be effective against the harbor and the airfields) the strike force will have to sit off Oahu for the entire day, recovering the second wave around sunset. Instead of the two waves being more or less continuous (1st Wave arrived at ~07:55, second wave arrived at ~08:40 IOTL making the attack seem almost nonstop), there will be a minimum 3.5, more likely 4.5 hours gap between the waves. That puts the second wave over Pearl around noon, IOTL the second wave took most of the losses, and tht was with everything being in a mad scramble. Coming back four hours later means ALL the Army AAA, the AAA on the undamaged ships (including several battleships and cruisers) and undamaged fighters (3 F4F, 27 P-40, 16 P-36, and, God spare them, 14 P-26) are ready and waiting.
Four decks is unlikely, but on the outer edge of possible, for much the same reasons laid out above, although an extra deck allows two weaker waves with the same sort of timing as IOTL. Damage is likely to be far less severe two two under strength waves (as was only 8 of 49 converted 14" shells managed to hit a ship during the first wave, 1/3 fewer aircraft mean the early AAA has fewer targets to deal with, and the second wave runs into a relative buzzsaw).
Almost as important is the fact that the
Kido Butai had additional tasks, including supporting the landings on Rabaul. Although not part of the original IJN planning, two-three fewer decks means the second attempt at Wake either doesn't happen or fails when the U.S. relief force shows up. The damage that does to the Japanese war plan is enormous.