The 11 core pages contain scripts that provide the functionality of MemberMouse. If more core pages are added, they, too, have the same functionality, but the base 11 core pages are required and should not be deleted. If they were, you will definitely need them in order for the plugin to function properly.
Good news is that they're easy to restore if you have not deleted them from your trash.
You can restore your core pages by going to MemberMouse > General Settings > Manage Install > Repair Core Pages.
Now, you should be able to return to building your site, all pages intact. If your core pages were not restored somehow, please submit a ticket to customer support, and we'll work with you to resolve the issue.