I can make a case for any of several things from the written rules, but I can't make a strong enough case for any given case to rule out the others, in general. Jeremy's answer is the simplest; just tell people what the intent is, and everything's solved. (I think this applies equally to any and all other polymorph effects, too.)
Interesting related note, I believe one of the designers said that the intent was that if you hold a True Polymorph long enough for it to become "permanent", you lose the revert-at-0 thing; it's just your new form now.
Seebs, you have stated a position in this debate, but your posts actually undercut your own stated intent.
Your stated position is that the rules in question, the words that are written, could reasonably be interpreted either way. Given this, you should be arguing against those who claim the words can only be understood one way and support (or at least not counter) those who agree that they could be understood in two ways.
Nothing wrong so far.
But Maxperson continues to assert that the words can only be interpreted one way, but you say nothing to him.
I agree with you that the words could, on their face, be understood either way. But which way is the right way? They cannot both be correct, even if the wording leads to ambiguity
So I
then explore
both interpretations, and reach, through reason, that only one of the interpretations stand up to scrutiny. And yet you criticise me (erroneously) by accusing me of denying that the words could have two interpretations.
Using reason to explore each interpretation to get an answer is the only way forward in cases where the text is ambiguous like this (unless you ask the writer-which we did!). It is not 'making up new rules' when you use logic to understand that a rule 'cannot' mean A, therefore B, however unlikely, must be true.
We know that Wild Shape rules that, when you take damage, you revert to druid form at 0 hp. We know that, at 0 hp, you fall unconscious/die. The game includes effects that remove their own trigger, like
shield or the orc/barbarian abilites, that mean the trigger condition is replaced by a different condition. But is Wild Shape like that? If it isn't, then the beast form dropping to zero would cause unconsciousness/death by massive damage, and
also revert the druid. But this does not happen. So, logically, it
must be that the reversion to druid happens
instead of, rather than
in addition to, falling to 0 hp. The druid doesn't actually die and then
heal to his druid hp total; his beast form goes away and his true form gets damaged. There is no healing involved.
The logical extrapolation of existing rules is a different thing than 'just making stuff up'.