I would start by looking through the plugins source code for two strings.
register_activation_hook
register_deactivation_hook
I'm on a system with grep available so I would use something like this via SSH to find those calls, assuming I'd already changed my CWD to the plugin folder.
grep -r -n -i 'register_deactivation_hook' .
Running that on the last plugin I wrote would return the following.
joebert@ubuntubert-2:~/$ grep -r -n -i 'register_deactivation_hook' .
./autobox.php:422: register_deactivation_hook(__FILE__, array(autobox_wp, 'deactivate'));
joebert@ubuntubert-2:~/$
- joebert@ubuntubert-2:~/$ grep -r -n -i 'register_deactivation_hook' .
- ./autobox.php:422: register_deactivation_hook(__FILE__, array(autobox_wp, 'deactivate'));
- joebert@ubuntubert-2:~/$
Which tells me that Wordpress is supposed to execute the "deactivate" method of the "autobox_wp" class when the plugin is un-installed. It would be similar for the activation_hook.
Then I would go through those files and see what the plugin changed when it was being installed. Maybe I can just change a couple of database flags manually real quick, maybe I can quickly delete some database values and revert a file or three to backups in order to reset my Wordpress installation to before the plugin was installed.
This is of course assuming the plugin sticks with the plan and only modifies the Wordpress installation during activation and deactivation.
Strong with this one, the sudo is.