Say you have an Amulet of Health +2 and you're level 10, so it's giving you 10 HP. Wild Shape says this:
Any gear worn or carried by the druid melds into the new form and
becomes nonfunctional.
However, Alternate Form (which what Wild Shape follows), says this:
The creature gains the physical ability scores (Str, Dex, Con) of its
new form. It retains the mental ability scores (Int, Wis, Cha) of its
original form. Apply any changed physical ability score modifiers in
all appropriate areas with one exception: the creature retains the hit
points of its original form despite any change to its Constitution.
Given that, I've got a player making the case that because HP stays fixed when you Wild Shape, it stays as it was when the item was active. That is, he keeps the +10.
It seems to make more sense to me that the Amulet would deactivate and you'd lose the bonus HP from it, and then your HP stays at whatever it would be at that point (since it's not adjusted to the CON of your new form). That is, he loses the +10. In this case, a Wildling Clasp would let the Amulet continue working and thus he'd keep the +10, which is how pretty much every other item works (and I do like consistency).
Any suggestions on which one it is?
Best Answer
Your player is correct; the rule says your HP stays the same so your HP stays the same. The game very rarely (and only very awkwardly) cares why a particular statistic has the value it does; it just cares what the value is. In other words, when it says the hit points of your original form, it just means before using Wild Shape, including the item (and spell effects and so on).
Note that this does not invalidate the rule that the item is melded into the character and deactivated. That still happens. The character does not have a magical enhancement bonus to Constitution while Wild Shaped, and his Constitution (for the purposes of Fortitude saves, Concentration checks, and so on) is what it would normally be for that animal.
It is despite those facts that the HP remains what it was before the Wild Shape, including the HP due to the higher Constitution that the amulet of health granted. When you Wild Shape, your Constitution changes: your new form has a different Constitution, and the amulet of health is deactivated. Nevertheless, your HP is not affected by these changes in Constitution.
If it matters to you, though, just houserule it and maybe give the player the opportunity to swap the Amulet of Health with something else if they like. You’re right that it seems odd to “benefit” from a deactivated item. And the druid is plenty powerful enough without that option.