redirect pages with no content, instead of 404 error, using max_num_posts?

If the rest of your function works you just need to add a call to wp_safe_redirect and hook the whole thing into WordPress. I think that the first hook that will have a populated $wp_query is wp. So alter the last part of your function…

if($max_page < $paged){
    wp_safe_redirect(get_bloginof('url'),'301');
}

And then add the following after (outside) the function.

add_action('wp','redirect_tags');

I think that should do it. You can setup infinite redirect loops so be careful.

Edit: The problem is the is_paged() check at the top of your function. If you try to access a pagination page that doesn’t exist is_paged() returns false and none of the rest of your function runs. Remove that check, and hook to template_redirect. I tested this and it does work. In other words…

function redirect_tags() {
  if (is_main_query() && !is_singular() ) {
    global $wp_query;
    $paged = intval(get_query_var('paged'));
    $max_page = $wp_query->max_num_pages;
    if ( ($max_page < $paged) ) {
      wp_safe_redirect(get_bloginfo('url'),'301');
    }
  }
}
add_filter('template_redirect','redirect_tags');