Disgracefuly Failure vs Graceful Failure

If I have a site running with this installed, and grab a copy of it, then set the copy up on a local machine or VM that does not have memcached, I would expect to be told so.

Instead I have a white screen of death and have to pull up an error log to figure out what might have gone wrong

This is easily fixed with:

if ( !class_exists( 'Memcache' ) )
    wp_die( 'A memcached object-cache drop-in is installed, but no memcache is available' );

You may prefer to also check if WP_DEBUG is defined or not, or call error_log

https://www.ads-software.com/plugins/memcached/