The Linchpin User Profile installation won't destroy the old Confluence user profiles structure.
Synchronized profile fields
Confluence itself contains a couple of default profile fields. When you install Linchpin User Profiles, all values that exist in these default fields will be migrated to the respective Linchpin User Profiles fields.
As long as the Linchpin User Profiles app is activated, all profile field data is managed by it. Nevertheless, all changes to migrated fields will be kept in sync with the default Confluence fields. So if you need to disable or uninstall Linchpin User Profiles, the Confluence profile fields will still be up to date.