prestongilstrap:

Cerebrates are still part of The Swarm, just not the swarm under Kerrigan's command. They're part of the rennegade broods and likewise.

This is the only place you are wrong. Cerebrates have been confirmed by Blizzard to have died out without the continued presence of an Overmind.

the Oceanborn:

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The only problem with this is that the Flood doesn't change the host's DNA. Kerrigan was genetically altered, and retained consciousness. The Flood is parasitic. They burrow into the victim, absorb knowledge and calcium, destroying the body in the process.

Actually, Guilty Spark mentioned that the Flood do change their hosts genetically, in the Library.

Lethe:

Then you should be pretty happy with the game; it's a lot of fun.
Even if a squad of marines out of dozens of units on a battle field has shoulder pads .25" too thick for a fanboy's tastes :)