Sorry to know that you are having issues with the plugin.
First, did you selected the require element for your header ? The font are assigned those element as selected from the plugin admin page.
Second, after deactivating the plugin or removing the font, the fonts should get back to the original. Are you using Cache or Minify plugin, You might need to flush the cache plugin after changing the font.
If you could provide me your site url ? I could check better for you.