I can see a lot of virtue in retaining some position coaches from the perspective of a new head coach. For one, it gives some continuity to the current players and recruits, and the position coaches would help the new coach assimilate into the university. The other virtue is that position coaches can usually be terminated later without too much fuss and thus there is little risk in retaining a position coach or two from an out-going coaching staff.
I could see a lot of utility to keeping Brown, since he is an institution unto himself at Nebraska and would make an ideal ambassador between the current players and a new coach. His experience at Nebraska also transcends his time as a Pelini assistant, so he might not feel the undying loyalty to Pelini that the Becks, Papuchises, Kazes, etc. might feel. He also has the capability to coach a variety of positions (TE, RB, etc.).
Warren seems like a high-character guy, a good recruiter, and has a short history with Pelini, so he, too, might not be poisoned by Pelini's "F everyone but me and mine" mentality.