I don't know if this is specific to the GCAL plugin or not but when I try to delete 1 (of 4) instance of the GCAL II plugin I get the question to completely remove the Plugin. I believe it should not happen unless it's the last instance that I'm trying to delete.
If I answer "Cancel" then nothing will get deleted. If I answer "OK" the plugin will uninstall completely together with all the instances.