The text you quoted defines death attacks (as a keyword); also known as death effects. It tells us what usually death attacks are and which special rules govern them.
However it does not say that all abilities that share some features with death effects are death effects. The Assassin's Death Attack shares some features with the most common death effects, but is not explicitly marked as a death effect.
By contrary, the Death domain granted power is explicitly described as a death effect (so the victim cannot be raised through Raise Dead, and Death Ward protects against it).
So, no. A victim of the Assassin's Death Attack could be resurrected normally by the Raise Dead spell.
That said, the lack of a death effect descriptor to the Assassin's Death Attack could be a minor design flaw that slipped through various editions (3.0, 3.5 and even in Pathfinder). I'd feel confident in house ruling it as regular death effect.
Intellect Devourer magically consumes the brain of the victim. Once it leaves, there's just an empty hole where the brain used to be.
To quote the monster description:
the intellect devourer magically consumes the target’s brain
Death Ward, on the other hand, prevents the subject from dropping to 0 HP - it drops to 1 HP instead. So while under DW, the Intellect Devourer is actually protected from ejection, if it indeed gets inside in the first place.
Once it leaves the brain has to be grown back in one round, or the subject dies.
"The body then dies, unless its brain is restored within 1 round."
I was about to write how DW would not protect the victim from dying because of a lack of a brain, but then it struck me that as a DM, I would probably rule that "magically removing someone's brain" would fall into the "effect that would kill it instantly" -category which DW protects the subject from.
Mostly because, while the body is still living under the Intellect Devourer's control, there's nothing of the victim left; no memories, intellect, etc.
(Which opens a whole new can of worms in the form of "brain vs soul" -discussion which is open to many interpretations...)
So how DW works in this case (without finding any official ruling on the matter saying otherwise), in my opinion, would be that the Intellect Devourer could not remove a target's brain and enter it, if the target was under DW's protection (which would then end DW and leave the target open for another try, later on).
Best Answer
Probably not.
Death Ward protects against:
The normal way that the rules determine what spells are included in categorical descriptions like this is using the descriptor system. Descriptors are tags found in spell descriptions that describe what kind of spell they are. According to the rules:
In other words, these things exist specifically to tell you stuff like whether Death Ward will protect you from Implosion. And there is, in fact, a [Death] descriptor, that gets applied to instant death spells. For instance, take a look at Finger of Death.
Implosion does not have the [Death] descriptor. That suggests to me that it is not blocked by Death Ward.
I've also seen it argued that Implosion, despite not having the [Death] descriptor, squeaks its way into the protected category by counting as a "magical death effect," based on the definition of "Death Attacks" in the rules for special abilities:
This description does sort of match the effects of Implosion if you squint. However, this is in the rules for Special Attacks (a subcategory of Special Abilities, things you might see in a monster's stat block). In my opinion, this means it is not applicable to spells, and has no impact on the interaction between Death Ward and Implosion.