Vorpal and Warshaper, immune or not?

Question

I have a question regarding Vorpal and the Warshaper ability, morphic immunities. Let's first look at Vorpal (SRD, emphasis mine):

Vorpal: This potent and feared ability allows the weapon to sever the heads of those it strikes. Upon a roll of natural 20 (followed by a successful roll to confirm the critical hit), the weapon severs the opponent’s head (if it has one) from its body. Some creatures, such as many aberrations and all oozes, have no heads. Others, such as golems and undead creatures other than vampires, are not affected by the loss of their heads. Most other creatures, however, die when their heads are cut off. A vorpal weapon must be a slashing weapon. (If you roll this property randomly for an inappropriate weapon, reroll.)

Strong necromancy and transmutation; CL 18th; Craft Magical Arms and Armor, circle of death, keen edge; Price +5 bonus.

Next, let's look at the Morphic Immunities ability from the warshaper (emphasis mine):

Morphic Immunities (Ex): A warshaper is adept at distributing her form's vital organs around her body to keep them safe from harm. Warshapers are immune to stunning and critical hits.

I have always read this as that a warshaper (or anything else with crit immunity) is immune to the vorpal effect, because the crit can not be confirmed.

However, my DM is claiming that even if you are crit immune you can still lose your head (based on the bolded part in the vorpal description). He reasons that if a skeleton can lose it's head, while being crit immune, then crit immune doesn't protect against vorpal.

Therefore, my questions:

1. Is he over reading the (what I assume to be) fluff part of the description, or is he right?
2. If he is right, would the bolded part of the Warshaper result in a headless (but still very much alive) Warshaper (by moving vital organs (brain)) into it's main body?

Answer 1

Your DM is right. Vorpal explicitly works on vampires, which are also immune to critical hits, so being immune to critical hits (whether that’s with Morphic Immunities or with heavy fortification or whatever else) is not enough to be immune to vorpal. Your DM could accept the portion of Morphic Immunities that you’ve bolded as justification for not needing your head, but that’s pure description and insufficient to justify, as a player, that he should. For instance, moving something vital out of the way of a sword-thrust might be possible, but maybe it doesn’t work fast enough to move everything out of the head before the head is lopped off.

On the other hand, a warshaper may be able to justify simply removing their own head as a precaution: move everything you need into your torso, morph away your head (or leave it remaining as a fleshy diversion, as many animals do?). That would be a discussion to have with your DM.

Answer 2

RAW says you're immune, but this is a case of rules not matching flavor.

How Vorpal works:

1. Roll a natural 20.
2. Confirm critical hit.
3. Heads roll.

However, Morphic Immunity says that you're immune to Critical Hits. So what's a Critical Hit in 3.5e?

When you make an attack roll and get a natural 20 (the d20 shows 20), you hit regardless of your target’s Armor Class, and you have scored a threat. The hit might be a critical hit (or "crit"). To find out if it’s a critical hit, you immediately make a critical roll—another attack roll with all the same modifiers as the attack roll you just made. If the critical roll also results in a hit against the target’s AC, your original hit is a critical hit. (The critical roll just needs to hit to give you a crit. It doesn’t need to come up 20 again.) If the critical roll is a miss, then your hit is just a regular hit.

Emphasis mine.

So a Critical Hit is when you confirm your threat roll. There are several kinds of monsters that are immune to critical hits. These are: Constructs, Elementals, Oozes, Plants, Undead and Swarms. The first four often do not have heads or have them as whims, the fifth is mentioned in your first quote and the sixth doesn't work like a single monster. This means that you don't even get to roll to see if you scored a critical hit: a natural 20 is just that.

Do note the mentioning of vampires in the quote for Vorpal weapons. Despite them being Undead they are specifically mentioned to NOT be immune to Vorpal weapons. This is possibly based on vampires of lore who traditionally die from having their heads cut off. But 3.5e vampires are immune to all other critical hits, just not the ones from a Vorpal weapon.

So how does this affect the Warshaper?

Given that vampires are not immune to Vorpal weapons because they are mentioned by name in the rules for the ability instead of saying "things that are normally immune to critical hits but have a head that can be severed are not immune to critical hits from a Vorpal weapon", the Warshaper is in fact immune to Vorpal weapons. However, given the reason why Vampires are vulnerable to it (getting their head chopped off kills them), it could be argued that a Warshaper is not immune because getting their head chopped off kills regular humanoids just fine.

To avoid dying from having your head cut off you have to move down the two most vital parts: the brain and the spine. Even if the Warshaper can pull down their spine and slurp their brains into their chest having their head cut off will still be a problem because you just lost a majority of your senses. So unless you move your face down to your torso and walk around like a pseudo-Krang the Conquerer (make sure to dress for this if you want to see, though!) or pull it in like you're a turtle and fight like that (and how will you see?), you're going to have your head sticking out. You could say something like you got a bone structure around your neck that prevents viking crew cuts, but that still has your head on display. Do be wary of the roleplaying repercussions of walking around without a head though.