Woah, slow down there... we don't want you leaving us!
But say you were to deactivate, if you were using live mode, your site will resume serving the significantly slower, unoptimized images. Your images will remain in the previous state before WP Compress was added.
If you've locally compressed images, the smaller optimized images are saved on your server and if you were to deactivate the plugin, they'd maintain the current state. You may restore them for up to 14 days after deactivation, so if you're interested in restoring then please do so before deactivating.
Updated on: 02 / 10 / 2021