Does this need to be a humanoid rig? Are you planning on using any humanoid specific animations, or is this a general character that has animations specific to this rig? If it can be a generic rig then use that. Humanoid rigs require that you have all the available bones, if the head bone is not available with your model then you can’t use the humanoid rig. Here are some more links that can help you out: https://docs.unity3d.com/Manual/BlenderAndRigify.html
and if you need to use a special package there’s also this free one on the asset store: https://www.assetstore.unity3d.com/en/#!/content/735
I don’t have much experience using Rigify rigs with Unity, usually my rigs are fairly simple and/or created outside of Blender.
