Just a reminder: Gahz'rooki will no longer be purchasable once 5.4 is released. Instead, it will turn into a rare drop that you have a chance of looting from "Kor’kron, and other associated mobs in Northern Barrens." Here's the official announcement
So if you're not interested in hunting for a rare drop, be sure to head out to the Barrens before 5.4 hits. Keep in mind that the pet is cageable, so you could also check the AH. This means you can also stock up on extra Gahz'rooki(s) to give to friends/family who may not have been around for the Darkspear Rebellion, or even sell them on the AH once the next patch arrives.
Collect now or later. Whichever way suits you best.