None of the assistants were let go other than Grantham who was "allowed" to take another job. I think it was pretty clear that Rizzi thought he was doing a bad job and promoted Young over him which lead to Grantham taking another job. But Loomis did say they are all allowed to interview for other jobs and we know that Kubiak has done so.
But, it probably does make sense to keep the guys around that we can to see if the next HC or coordinators want to work with those guys. Despite the results and as much as I want a total reset, we do have some good coaches on the staff such as Hodges, Young, Dennison, Benton, Galliano, and the WR coach we got from the Ravens. They just had a terrible leader in DA. Rizzi is also obviously a good special teams coach, but I think the only chance he stays is if he gets the HC job or if McCarthy is hired. McCarthy given his experience might not feel threatened by having the former interim HC on the staff the way a young coach might.