Yeah, Rift Mage as a specialization is gone as far as future games are concerned. Remember the Breach altered how magic normally worked as long as it was around.
I wouldn't count on it in regards to and Inquisitor themselves as the Breach had been two years gone prior to the events of "Trespasser" and yet the Inquisitor still retained their Rift Mage Abilities. From how I understood Rift magic, its a new field of study that focuses the raw energy of the Fade into substantive forms. So rather than using Magic in order to create varying elemental effects (fire, lightning and so forth) you are channeling the "element" that is the Fade itself (Cole mentions something similar if you talk to him about it). 
From the dialogue that you have with "Your teacher" it seemed that the fundamental difficulties in learning Rift Magic was that in order to start learning it a person required direct contact physically with the Fade itself (most commonly through a Rift), which drove most of those trying to learn it insane, or outright killed them. While I'm sure the Anchor helped this process for the Quizzy the fact that others (including Your Teacher as bonkers as she was) were capable of channeling that energy of the Fade without such an advantage proves that at least, in some capacity, it can be used without the Anchor. Even if you take away the Anchor from the Inquisitor that physical exposure has already occurred (its like a gate or an initiation) as the Inquisitor has been thrust into the Fade physically two (if you have OGB, three) times already. Granted a Rift Mage Inquisitor (like any Inquisitor) will still have to reteach themselves to fight in order to compensate for the missing limb.
Though, if you were to ask me if the Rift Mage Specialization will return in future games (assuming the Inquisitor themselves will not be playable in any form), then ... no. The Inquisitor is Unique in that it was the Anchor that allowed their retained sanity or survival during training. They have already survived that training with their health and sanity intact so presumably they should still have the power, but no-one else is going to have access the shortcuts or advantages that the Quizzy had. Trying to self-teach Rift Mage specialization from a Venatori Tomb would be absurdly dangerous. 