I haven't looked at the plugin specifically, but what plugins usually do is that they modify the markup and then attach event listeners to it.
For example, a content editor may create a few buttons like "bold", "italic" etc. and then attach a click event to each button. At a click, it will add [b] ... [/b] to a textarea for example which is also given by the defined markup.
What you can do to "deactivate" this plugin, then, is to reset the markup. To do this, first use the jquery remove function to remove all markup that has been created (it should have been put inside a container so it should be easy and quick) and then append again the required markup that you had from the beginning. This markup will not be affected by whatever listeners had been created earlier.