How check that there is post thumbnail feature image or not on wordpress?

Question

The main problem here is what exactly was removed. If only thumbnails, then you can always regenerate them and everything should work OK.

If all files are missing, then you can check if attached file is missing using this code:

if ( file_exists( get_attached_file ( get_post_thumbnail_id( $post_id ) ) ) {
    // file exists
} else {
    // file doesn’t exist
}

You can also use wp_attachment_is_image function for that:

if ( wp_attachment_is_image ( get_post_thumbnail_id( $post_id ) ) {
    // file exists
} else {
    // file doesn’t exist
}