Please consider that All of the WordPress dynamic data is stored in a MySql Database, not in any theme files. So, you will not loss anything like posts, pages, menus, settings etc.
WordPress Menus are controlled by WordPress Core, not by our Themes. It is WordPress System that when you install and activate any new theme, WordPress shows the pages as the Menu Items. You can set your own Menus from WP-Admin > Appearance > Menus > Menu Locations. It is a 2/3 mouse clicks matter.
You need not re-do anything. All are stored in your database. Don’t worry please. In Small Business Extend you can select which posts can be shown in Slide and Blog Index of Front Page. All posts/pages may not be important. Please follow This Article for Slide Setting.
BTW, what is your Site URL ?
