Please note that we've updated the Mount & Blade II: Bannerlord save file system which requires you to take certain steps in order for your save files to be compatible with e1.7.1 and any later updates. You can find the instructions here.
There's Dismemberment mod. Good idea, but in fact decapitation looks weird. We only can make meshes invisible but we can't remove head collision capsule. And when we'll try to place new head instead old it appears nearby. In slow motion mode it can be seen clearly.