There is couple problems:

Critical hit BUG with cold table
Critical hit BUG with holy table

Also, it would be great if I get good XP for severing crits. Suppose, if I severed NPC head I would consider it as IK and get as much XP if that was SQUISH, for example.

There is no critical filter. So, if NPC has no hands anymore, you still get singing critial that should blow off mob hands. Either do not let it happens anymore, or just do not show it (like no critical was happen at all).