Hook_menu() and its page callback: how to redirect users on a condition?
If you are altering a hook_menu item that an existing module defines, use hook_menu_alter. You will receive all menu items by reference, and you can alter the necessary menu items as necessary. 

In a hook_menu() implementation, if you define example path, http://example.com/example, http://example.com/example/foo, http://example.com/example/foo/bar... and so on will have the same page callback and other properties. However, if you define http://example.com/example/foo/mine, that page will use the explicit definition of example/foo/mine. There is a negotiation with MENU_DEFAULT_LOCAL_TASK too. 

PS: If you are trying to redirect comment pages to their node paths, try this module.