Some Facts...Some REALLY WISHFUL Thinking as well
It is my hope and great wish that Scholasticate questline remains a solo act from the returning of Hildiabrand personally. I like it and I also like that we get a serious investigation over Hildi's antics.
My really wishful thinking is that we get sent back to Big Bridge and find that its finished and we get new area's to explore while tracking him down to watch Golbert piledrive him again!. I do believe that the Hildi and Giga are permentantly link.
Based on current side storys inside ishgard, the thief isn't hunting Hildi, but playing the Scholasticate questlines, I think the thief has decided who his/her true rival is, and it ain't Hildibrand.