Removing a squarespace member area but keeping the pages behind it

After you move them, open each page's settings and check the URL slug didn't change. If it did, any links you've shared and anything Google has indexed will 404, so either change it back or add a redirect under URL mappings.

Take the pages out of the member area before you delete anything. The member area settings list the pages it restricts. Remove them from that list so they become public, and check them in a logged out or private window. Only then cancel or delete the member area. If you charge for access, sort out the existing members' plans first so nobody gets billed for a members area that's gone. And if you aren't sure what deleting it does to those pages, duplicate them first. That costs nothing.