Was destroying BOTH Lando's and Wedge's targets necessary to blow up the second Death Star?

Question

At the climax of Return of the Jedi, Lando Calrissian and Wedge Antilles each strike a different target when they reach the core of the second Death Star:

Rebel pilots Wedge Antilles and Lando Calrissian fly into the reactor core, with Antilles in his X-wing first taking out the power regulator with proton torpedoes, and Calrissian captaining the Millennium Falcon to strike the main reactor with concussion missiles, which sets off a chain reaction that destroys the battle station.

Wikipedia

Was it strictly necessary to strike both of these targets? What would have happened if only one of these had been destroyed?

Answer 1

Apparently, yes. According to the (canon) Star Wars: Battles That Changed the Galaxy factbook, Wedge's destruction of the power regulator was instrumental in the reactor exploding.

A Chain Reaction:

Wedge Antilles destroyed the Death Star's power regulator, meaning that when General Calrissian opened fire on the reactor itself it suffered a catastrophic collapse. A huge explosion was inevitable.

This is echoed by Wedge's Biography Gallery on the StarWars.com website

Once Han’s commandos brought down the shield generator protecting the Death Star. Wedge flew into the battle station's superstructure. He followed the Millennium Falcon into the heart of the Imperial superweapon and fired a proton torpedo into the main reactor’s power regulator, helping start the chain reaction that destroyed the station.

The implication seems to be that if the reactor could regulate its power properly, it wouldn't have exploded when damaged, it would have just shut down or fizzled.

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The Official Star Wars Fact Files #113 is also similarly certain that both elements were required in order to create the devastating cascade failure that blew up the Death Star II. Interestingly, it refers to each of the attacks as 'laser fire' rather than 'missile fire', but we can probably chalk this down to writer's error.

FIRST BLOOD:

When the Rebels attacked the second Death Star, they targeted the north tower first. This contained the power regulator, which channelled off excess power. If this facility had remained operative, the Rebels' laser fire could have been absorbed and its assault would have been unsuccessful.

ENDGAME:

With the north tower destroyed by laser fire, the Rebels made a frantic escape. Their assault had started a chain reaction, releasing the reactor's enormous power which soon destroyed the second Death Star from within.

KILLER BLOW:

The floor, ceiling and walls of the vast chamber were covered in power conduits that carried the energy from the reactor to various parts of the battle station. These were one means of absorbing power surges from the reactor, Another was the power regulator built into the north tower. This extended from the side of the tower and served to channel off excess power. It was this feature that the Rebel strike team hit first. If it had been left intact, the power regulator could have absorbed the energy of the Millennium Falcon's lasers. As it was, just a few laser blasts set off a catastrophic collapse in the central contact space. This brought the north tower crashing into the chamber. From this point' on, the Death Star was doomed. Within a few seconds, a chain reaction released the vast power within the reactor, and the battle station was reduced to ashes.

Answer 2

I understand it like this:

If you blow up Wedge's target (the regulator), but not Lando's (the reactor), there's no big boom and the Death Star stays intact. You may have succeeded in disabling some systems like the giant superlaser or hyperdrive until the regulator is replaced/repaired. However, it's not obvious which systems (if any) would function and which would not, especially as the term "main" reactor implies additional smaller reactors providing energy for some systems.

If you blow up Lando's target (the reactor) but not Wedge's (the regulator), there's a big boom when the reactor blows, but the regulator somehow dissipates the energy. Either way, you've definitely disabled the Death Star, as the main source of energy is gone, but the reactor can be replaced/repaired without starting over constructing the entire thing from scratch.

Alternatively, without first destroying the regulator it's possible the containment and shielding system mean to contain the reactor's power would have prevented the destruction of the reactor at all with only the armaments available on ships small enough to fit inside the superstructure.