
Originally Posted by
Mislagnissa
I think I discussed this before but here is a quick refresher.
The manual introduced the Overmind as a gestalt consciousness of the Zerg. Cerebrates are a breed created to increase efficiency by managing broods. If killed, cerebrates may be resurrected or reincarnated unless they are killed by the nerazim's void magic. In SC2 Kerry is resurrected in the same way, so it may be assumed that all Zerg personalities may be so revived even without the Overmind. (It is not explained where they store their backups, but if this follows the same logic as the Overmind then these personalities are stored within the broods.)
The EN chronology follows this exactly, but it adds two additional rules: broods are only successfully managed by giant brain-like creatures (e.g. cerebrates, giga-brains, psi colonies), and the broods are instinctively driven to recreate the Overmind after its death by dominating their competition. Aside from psychic power levels, the biggest difference between the cerebrates and the assimilated terran brain monsters is that the latter lack the accumulated wisdom and knowledge of the former. Otherwise they are both Zerg monsters driven to consume and evolve.
Something I am going to borrow from the Flood and Necromorphs is to apply the logic behind the Overmind to the broods individually. The Zerg are organized into a hierarchy of hive minds that follow the same basic logic. The Overmind is the hive mind of the entire Zerg race, while each brood has its own hive mind which is broadcast by the cerebrates like radio towers.
Zerg have two layers of psychic communion, as originally stated in the manual. The first is a psychic link between the Overmind/cerebrates and all their minions (and possibly between minions?), whose purpose is not explained. The second is the active relaying of orders from the Overmind to the cerebrates, to the overlords/queens/infestors, to the minions. These are not interchangeable functions.
The Zerg have undergone refinement over the millennia, which includes the equivalent of lobotomizing non-essential higher brain functions that are normally invisible. Since the Zerg operate under a hive mind where brain function is shared, they do not need to be able to function outside of it. Zerg which are unable to connect to the hive mind (such as in captivity) will act strangely and without any self-awareness, regardless of whether their intelligence matches or surpasses that of a human being, since they have essentially lost key brain function: minions will become rabid berserkers, overlords will repetitively follow their last orders, queens will churn out minions that immediately turn feral, etc.
Normally this is not a problem since the Zerg will naturally commune with other nearby Zerg to make up for their individual lack of awareness. When a cerebrate is killed, their telepathy allows the brood to retain some degree of coordination (albeit vastly inferior) until the cerebrate is respawned. Void magic does not simply sever the brood from the cerebrate's control, but traumatizes the psyche of the Zerg that composed the brood so that they cannot simply restablish the hive mind as they do when cerebrates are killed without void magic.
EN makes a distinction between feral zerg (broods that have lost their cerebrates) and insane zerg (broods whose cerebrates have lost the overmind), but under the overmind=hivemind logic this distinction becomes mostly a matter of semantics. In the same way that the broods as a whole are driven to recreate the Overmind, broods which have lost their cerebrates and survived are driven to recreate it.
In Protoss space, where psi colonies and giga brains were deployed in large numbers, these creatures are driven to claim control over the feral broods formerly managed by cerebrates. Since this is a function they were never intended to fulfill, they are not able to easily access the memories or personality fragments of dead cerebrates that may be preserved in the brood.
Now is a concept of my own creation, inspired by BW custom campaigns: Most broods that are rendered leaderless will destroy themselves. Those broods that survive without cerebrates or assimilated terran commanders will eventually spawn new cerebrates. These cerebrates, or neo-minds if one prefers, operate at a distinct disadvantage because their memories are fragmented by the trauma inflicted through void magic. Like all Zerg intelligences, they are driven to dominate their environment and by extension to recreate the Overmind. They may be more closely compared to the Flood or Necromorphs in personality than other Zerg.
That is not all. Without the Overmind to regulate the Swarm, there is nothing preventing broods from accessing (or modifying) the genomes for cerebrates, miniature overminds, and other brain-like organisms contained within the larvae. While in practice this will not allow any single brood to instantly win the brood wars by creating an avatar for the Overmind (who is too dead to make use of it), this knowledge is used to resurrect the Overmind. EN posits that after an unspecified period of time, the brood wars are brought to an end when an alliance of broods (a long story in itself) successfully creates the biggest brain monster ever (involving the fusion of many cerebrates in a way that mimics the creation of giga brains from humans) that successfully connects the hive minds of all Zerg in the galaxy at once and allows them to come to a consensus.
According to EN: the new Overmind is essentially the same person as the previous Overmind, since the Overmind is formed from the amalgamated minds of all Zerg in existence. That said, the trauma the Zerg suffered during the Great War and the Brood Wars has convinced the Zerg and the Overmind to (temporarily) set aside their quest for perfection in order to focus on immediate survival. The Terrans and Protoss, who by this time have enslaved many broods, developed anti-Zerg weaponry and are making diplomatic overtures to one another, present an existential threat to the Zerg. Before the Zerg can become perfect, these threats must be eliminated.
At that point the timeline for EN simply stops. I imagine that it ultimately ends in either a Zerg victory or the Zerg being destroyed, depending on the plot branch, since otherwise you would end up with Overmind/QoB/Amon/BigBadEvilGuy whack-a-mole.