What was 'specifically written' can be understood as either 'results in being reduced to 0 hp, and therefore unconscious or dead' OR 'when doing the maths of the game mechanics, the number ever gets to zero, even if it doesn't stay at zero'.
Apart from the drops/reduces question (which I don't think is a consistently-used terminology distinction), it seems to me that we have two fundamentally identical triggers: "[the druid] drops to 0 hit points" or "reduces [the target] to 0 hit points".
There's nothing to indicate that one of them means "ends up at 0 hit points after all other procs" and the other means "goes to 0 hit points at all ever".
So if an event can trigger one, that event can also trigger the other.
The maths and the game mechanics don't exist in the game world, they simply describe what does exist. Normally, being at 0 hp describes the game reality of being unconscious or dead (or as a trigger to revert). All of these things are events in the game world. Disintegrate triggers off the game world events of unconscious/dead.
No, it doesn't. It triggers off 0 hit points. If they had meant "triggers off the game world events of unconscious/dead", they would have written "if this damage knocks you unconscious or kills you".
The game mechanics of a druid's hp total as the beast form reach zero and switch to his normal hps aren't an event in the game world; the only actual event here is the reversion. There is no unconsciousness or death.
That's not stated, and it's actually not how I'd interpret it. I'd interpret it as being just like the trope in literature where you knock the shifter out, and they revert, except that they revert less damaged.
No, what he usually does is phrase his answers as his intent. He avoids language that restricts the choice of his players, to support his 'rulings not rules' philosophy. We shouldn't expect any other form of answer from him.
Agreed.
This is quite a feat of mental gymnastics: you ask him which it is, he says that the intent is that the druid survives (supporting the 'result' interpretation), and you pretend that he didn't answer your question because he didn't rule your way, using the excuse that his form of words didn't meet your standard.
See, I don't think the "result" thing is implied here, exactly. I think, rather, the issue here is that the wild shape (or other polymorph) powers are intended to interrupt damage processing and cause you to restart the damage processing with new circumstances; you apply the remaining damage to a new form, instead of continuing with the existing damage event. So it's not that disintegrate's relying on "final resulting damage"; disintegrate is as-written, just like unconscious/dead-at-zero is as-written, but the shape revert is an interrupt which breaks that.
That's simpler and consistent with the rules philosophy that you have relatively straight-forward rules and sometimes one rule trumps another.