Apostates are excommunicated members of the Invisible Church (the formal magical orders), though sometimes that so-called excommunication is self-imposed. They reject the other orders and even the idea of orders, existing outside those structures. Individualists, rebels, introverts, and castoffs, they find their own way by using bits of magic from each of the other orders, plus new discoveries they make. Sometimes while making rude gestures.
Apostates follow no single path. Rather, each Apostate has their own path—their own focus, specialization, and areas of expertise. They are explorers who eschew maps, blazing new trails, mostly for their own edification.
Likewise, obviously, Apostates have no organization or hierarchy. They are often quite unaware of each other. That is not to say, however, that Apostates are always loners, don’t have friends, or cannot learn to respect other vislae, even those who work within the system of magical orders.
Players who don’t want their character tied to any kind of organized structure might be interested in an Apostate. They lose access to some of the proprietary knowledge that the orders hold, but they gain the freedom to explore literally any sort of magic, or even invent their own.