this is just from the starcraft wikis, but, what's going on here?

Kerrigan is de-infested and then goes back and has to take over the Zerg again? Are they just not going to attack the humans anymore while they try and stop the prophecy?

wat

Zeratul realises kerrigan can only save us as queen, raynor let's her go back and reconvert, and she becomes queen of the swarm again to save the universe?

right, but he knew this before he converted her...

18+ months away

id say she can still control the zergs even de-zergified

She was a powerful psychic even before the zerg infestation (why they picked her to begin with) and judging by the cinematics the de-zergification isn't complete so I am betting she'll still be plenty powerful.

Maybe not quite as powerful but that would just mean an extra mission or two where we secure some random Psi Amplifier from the Dominion or steal some crystals from the Tal'darim nut jobs.

I'm not even sure de-zergification is quite correct. I really doubt the Xel'naga's artifact was created to reverse zerg infestations. I strongly suspect it made Kerrigan something more than a human/zerg hybrid. I would not be at all surprised if the artifact's primary function was giving the protoss "purity of form."

In essence, Kerrigan is (I suspect) basically some kind of super human with zerg's purity of essence, human body (for the X factor) and protoss' purity of form. In other words, she's the closest thing to a true Xel'naga in the galaxy.