I suggest 'strip_tags' filter before all strip_tags() function.
$after = strip_tags(apply_filters('strip_tags', $before, $context) );
In wp-includes/*.php, many code uses PHP's strip_tags() function. Most cases are fine, but the html using "del" elements meets a bad situation:
I left home <del>one hour</del><ins>two hours</ins> before.
I left home one hourtwo hours before.
The favorable result is removing del elements with inside text like below:
I left home two hours before.
In current WordPress code, it is little hard to creating a plugin that realize this behavior.
If there is a filter like above, we can write the plugin in easy way.