I would strongly consider Khari as a QB coach and a guy to help a new CO, like what Hall has done for JY. But I wouldn't go to him directly for an OC. Same role Jackson would play if we keep him imo.
Best case, you get both Costanza and Bourgoin as an OC/position coach, ast oc and position coach, and then still have a guy like Jackson as qb coach, keep Marty at that point, and you have the offensive staff wrapped up.
Between the two, I really like costanza as a unique football mind, not another lapo foot soldier. I think Bourgoin is better as a position coach, though, and more turnkey as an OC. I do think Bourgoin was likely much more responsible for the offensive success in BC than people would think, despite him working for Buck.
As far as retreads go, I would consider Lapo in a positional support coach role to a new OC. Despite being an original member of the fire plop train, I think he would do a great job helping a guy develop and coaching a position like WR. Pair Lapo, or jackson, or khari as assistant to OC Costanza, and you are in pretty good hands. It'd really come down to who the OC prefers and what they need.