The drop-in is removed, WP_CACHE comes back out of wp-config.php and the cache is cleared. The site goes back to exactly how it was.
On a multisite network, deactivating it on one site clears that site's cache and stops it being cached. The other sites keep theirs, so the drop-in and WP_CACHE stay until the plugin is deactivated on the last of them. Deactivating it for the whole network removes them for every site at once.
Still stuck? Ask the developers who wrote it. We aim to reply within one business day.
