Sadly the Path Companions I think are considered by SE as just a legacy of 1.0 now that Yoshi has moved away from. Save for some brief mention of them in the Minion Guide, they've been abandoned gameplay wise completely unfortunately, replaced by the Chocobo Companion and the new Grand Company Squadron. Story wise, the last we knew of their whereabouts was at the end of the last added Path of the Twelve quest in 1.0, 'Future's Perfect' (the one where Gaius was first introduced), where during the ill-fated mission to Mor Dhona the Path Companion ended up being shot by Gaius and was stated by Minfilia at the end of the quest as being sent to the ALC's Guild in Ul'dah for medical treatment... and that is the last we ever heard or saw of them.
It was originally intended to continue the Path of the Twelve storyline (evidence in 1.0's game files suggested that the player was intended to reunite with their Path Companion and be dispatched to Mount O'ghomoro to investigate the kobolds, and ending up encountering the Company of Heroes fighting Titan)... but a combination of the changeover in development team members (namely, Yoshi taking up position as producer and director) and the terrible 2011 Japan earthquake and tsunami saw to it that the Path of the Twelve storyline was pretty much abandoned at that point, the story instead changing to an emphasis on the approaching Seventh Umbral Era as part of the events leading up to the shutdown of 1.0 and the changeover to ARR.
Because of this, the Path Companions were also abandoned sadly, and, I think at this point now, it's safe to say they're not coming back (the story kind of handwaves it away anyway that most of the Path's members were killed in the Battle of Carteneau so it's highly likely that is where the Path Companion met their fate too - it's what I believe happened to my one in any event).