I created a custom post type name Blog. So when click the link [/index/blog/] all custom post types show there.
Now I deleted the custom post type Blog and created a page and named it "Blog". Now when I click the link it won't work. It won't show my page that I created. Since I deleted custom post type Blog, shouldn't show my page 'Blog' at [/index/blog/]?
Since you have created custom post type of name blog. Hence the slug blog is registered in database for custom post type. So it won't work for your page blog.
Edit the blog page from admin panel and check the Permalink which is just below the title. This is your link for blog page.