What happens if the plugin is deactivated after being used for a while?

WordPress will not automatically create the images that are “missing”. I believe the default action is to fall back to the first image it can use that is closest in size. So if the only image available is the original image, that is what will be served. If you are correctly using the WordPress media functions (wp_get_attachment_image(), the_post_thumbnail(), etc.) then the <img> tag should be correctly output with a height/width to scale the full-size image, but you would still be loading the full-size image.

There are a handful of thumbnail regen scripts around. I have used https://www.ads-software.com/extend/plugins/regenerate-thumbnails/ with some success, but depending on the size of your image archive you may need something different.

The dynamic image resizer actually creates the image files on demand, and those files will remain when the plugin is disabled.

However, this plugin is more of a proof-of-concept, and I do not recommend actually using it on a site. It’s a demo, not intended to be working code in all cases.

I realize you haven’t updated the code in a while (almost a full year now) but I think the concept is a good one, especially for image-heavy sites. Django has sorl-thumbnail and a few libs built off sorl that do similar things (https://github.com/SmileyChris/easy-thumbnails).

I looked around on github/bitbucket but didn’t find any repos that might be yours. If you were open to it there might be some interest in having a public repo where others can contribute and possibly bring something like this up to production standards.

I don’t really use git, and I don’t really care for github or bitbucket. If you want to contribute, patches are welcome.