According to documentation https://www.elastic.co/guide/en/elasticsearch/client/php-api/5.0/_connection_pool.html in official PHP client (https://github.com/elastic/elasticsearch-php), if a node fails then it will be marked as dead for 60*2^x (x - $failedPings) seconds. It seems to work during one request but during next request, each node is checked again.
Are these params preserved during the subsequent request? In the client, I do not see any usage of APCu or something that could save it for next request but maybe I'm missing something.