Inactive User - You shouldn't delete any categories and boards as it will impact on the ranking. My suggestion is just add the redirect to the new categories and boards from the old categories. Hope this will help you.
Give kudos if you find my posts helpful or mark solution if it answers your query.
Tariq
Keeping the boards/categories after shifting its content to new ones doesn't really make good sense. I really wish there was a better solution to it. Something like 'Maintain your SEO ranking while you delete the boards and categories'.
Thanks much TariqHussain.
