How to redirect 404s that generated for css&JS files?

Google crawlers just follow the HTML. If you intend on deleting CSS&JS files, search through all your themes&plugins that were using the files and either comment off or remove the line calling the CSS&JS files.

Look for both wp_register_???() and wp_enqueue_???().

Examples for plugins:

wp_enqueue_style('wp_css_name', plugins_url( '/assets/css/style.css' ... ));

wp_enqueue_script('wp_js_name', plugins_url( 'assets/js/script.js' ...)...);

Example for themes:

wp_register_style('normalize', get_template_directory_uri() . '/normalize.css'...);
wp_enqueue_style('normalize');

With all themes&plugins not calling for nonexistent files, your problem is solved.