The only reason to wear a mask is to protect an identity. A living, active or at least potentially active identity. Harry thought they were council and they were certainly powerful and knowledgeable enough to be so. The council is also the most logical source of powerful warlocks.
An identity is an identity, alive or dead. Kemmler is an identity and he is supposedly dead. So is Hitler. The status of their state of being isn't relevant. Simon was Council. Elaine is strong enough to be Council, but decieved the tests. And so on. Harry was blindly assuming that all the powerful wizards in the world were accounted for and on the White Council. Won't his face be red if he found out about powerful wizards that were not on the Council. Like Grevane and Corpsetaker. So logically, the Council is only potentially a source of powerful warlocks. There may well be others.
There seems a strong connection between the spiritual power of a wizard and his spirit. We also have not seen a death curse from anyone who returned or tried to return from dead. Kemmlers dead curse would have been devastating.
If Kemmler used a death curse. What's to say he didn't the first few times he was "killed"? And as one keen eyed fan pointed out, the Tsar Bomba (the most powerful man made nuclear warhead) exploded on Halloween, 1961. The same date Kemmler died. Which Jim acknowledged without agreeing with. Some guess that the bomb was dropped on him to kill him (or perhaps whatever he was trying to summon). Some guess that he completed the Darkhallow but was still mortal and the bomb was there to kill him. Some guess that there in fact was no bomb and that it was the cover story for Kemmler's immense Death Curse. Time will tell on that story.
But you
are speculating. It isn't a fact that Death Curses use up the energy required to come back. Jim hasn't EVER said that. So don't present such statements as fact.
The best alibi is actually a true one? The problem is that being dead actually reduces your options to act in the living world dramatically.
Yes of course. For example, in a mundane murder mystery the least likely person to have been the murderer was the person who was killed prior to the events. When it is discovered they haven't in fact died, everyone gasps and says "It couldn't be! That's impossible. You're dead!" or something along those lines. Same for Simon or whoever. Oldest trick in the book.
It only reduces your options to show your face. But if you are as disguised as Cowl is...I think it hardly matters.
Actually we do. Ghost story shows us how corpstaker was trying to return, Lea tells us actually how, and it probably was how Kemper managed it. She was his pupil after all. Find a body. Get the original owner out of it and take over. Harry had his own body to return to but for most dead that is not an option, too damaged.
We have Harry's perspective on a spell/ritual that he had little to no understanding of. He hasn't read how to do it, been told how to do it or even been taught how to do it. Lea tells us the basic components Corpsetaker will use. And of course that assumes that there is only one way to do it. Kemmler, Corpsetaker and Cowl are hardly the only people to do it. Although the Jury is out on Cowl. Harry didn't necessarily have the option to return to his body. Had Uriel not wanted Harry to roam free, upon Harry's "death" most likely he would have awoken to being Mab's knight and Demonreach's warden (and Bonea's father, but that's less a formal role). And how does one take over? Mind magic that Harry's has never been taught (and he is pretty bad at mind magic altogether).
When Harry had used up all his power at the end of ghost story and morty could not see him anymore he still had his soul. That is enough to go om but not enough to do anything meaningful in the spirit world.
That isn't necessarily true. Quite likely he would have diminished beyond that had Uriel not intervened. He also still had spirit left.
Their soul passes beyond. That is different from their spirit.
I am not going to get into another long debate on this (it happened in another thread somewhere) but I will say that again is pure conjecture. Soul and spirit have been used semi-interchangably in the books and in WOJ. What you just said isn't fact or gospel. Unless you have some proof somewhere that you can share?
There probably are but enough to risk it? You can try to return but it is difficult and tedious and success is far from guaranteed. I think we can safely assume that those few who do return from the dead did not arrange their own dead.
In point of fact, Harry himself arranged his own death. He might have been nudged but he did arrange it. It's not such a strange thing. People fake their deaths all the time. There are often strong financial incentives (either to escape debts or claim insurance), but also to escape convictions of crime, and probably other undesirable situations. The fact that Kemmler returned several times, and probably wasn't the first necromancer to do so suggests it isn't so strange. Corpsetaker may well have returned before, and it seems likely Cowl did at least once (if not more than once). I am not so sure that Grevane knew how to as we never saw him attempt it, but that doesn't mean he won't show up.
Not to mention those that don't actually die but are just percieved to die. The most common form of pseudocide (faking ones own death) is drowning as it leaves a plausible explanation for why there is no body.
On that, water grounds out magic and spirits can't handle it. Harry "died" in water. If the elements were such barriers wouldn't Harry have not been able to go out?
The problem is that there is the physical plane (earth) and the spiritual plane (the never-never). That's all we have so far. It seems reasonable that there is another layer to reality that normally Harry and other "alive" mortals cannot percieve even in the Never-never but permeates both Never-never and mortal physical plane. Let's call it the Ethereal plane. Each of these layers coexist on top of the other. So Harry's body anchors his soul. But his soul (and/or spirit) where never in the physical plane. The occupied the corosponding location in the Ethereal plane. This is both in and outside the Never-never. That much is clear from the fact that you could open a Way somewhere and not be in the Ethereal plane but be in a corrospinding Never-never location (like the FBI headquaters and the demnese of the Erlking). But over and through the FBI headquaters would still be that other part of reality, the Ethereal plane. GS makes this all pretty clear. It probably helps to have played some D&D or something. But each layer of reality both is on top of another layer and through that layer (yet unable to touch). An interesting example (although a bit different) was the show Fringe and there use of quatum mechanics. They both do AND don't occupy the same space, just in corrosponding universes.