It's pretty obvious that Collins will be the DC in all but name this season.
The only question left at this point imo is will Thacker still be the 'official' DC or will he be moved to a non coaching position or leave.
The more the days go by and we hear nothing it feels like Thacker will retain the DC title, but not have any coaching responsibilities, so that he and Collins can concentrate on defensive game planning. They could also simply be waiting until after the February signing period to announce anything as Thacker appears to be a good recruiter.
If Thacker does stay and does keep the DC title than that means special teams will have to be split amongst current coaches.
I'd be surprised if Thacker left GT completely as I think he and Collins are simply so close that Collins cannot even think of taking that step. I also think it is unlikely, though not impossible, he would be 'demoted' from a coaching position for the same reason.
FWIW, here is a statistical deep dive into the defensive performance for this past season. The overall story is that while the secondary was among the all-time worst, even the DL and the LB's did little to be impressed with.
Herein lies the autopsy report of the 2021 Georgia Tech Defense
www.fromtherumbleseat.com
That review is why if the thought is that the primary defensive problem was a horrible secondary and if we just fix that the defense will be ok than I am afraid it will be another long season. We need significant improvement at all 3 levels of the defense to be an adequate defense.