The coaching replacement MUST come from the outside. New, fresh voice. Someone who will implement a (trap) system that emphasizes defensive structure and support and insulates things in general. You let the offense flow from that.
I'd prefer Gallant, but it's got to be someone of that ilk. If it's an internal retread or someone with another message from the outside, kind of the 'we're still fast and skilled and we just are changing the voice for the sake of changing the voice', then it's over.
There's no guarantee that type of change is enough to turn the tide, because it's a lot easier to get a defensive team to open things up than it is to teach a team again how to play defense, but there's no way to evaluate and fix anything-- players, mix, etc-- without that type of coach being in there first.