To add this, you will need to override the following files:
At below code in Form.php, add:
The impact will be during that period of time(When ES is down) it may happen that Catalog Search results and Category Pages may not be accessible.
When Elasticsearch down then catalog_search index should be disabled for some time or switch to another search engine (i.e. MySQL).
For other items, it depends on a few other things as well