Profession questions

I'm currently a Skinner/leather worker, but I find I'm barely using the LW. I'm thinking of just switching to 2 gathering professions instead. So I have 2 questions:

  1. If I unlearn LW and decide to pick it up again later, will I need to start over or will my learned recipes still be available?

  2. Of skinning, mining and herbalism, which 2 give the best gold return from selling the mats?