Twenty eleven theme revert

My organization’s website (www.lincolncottage.org) runs on a very customized version of the Twenty Eleven theme, launched in the summer of 2012. Out of the blue, approximately 15 minutes ago the website reverted back to a basic, uncustomized version of the theme and is no longer navigable. I was not using the backend of WordPress when this happened, so I’m totally caught off guard as to what the issue might be and how best to resolve it. On a related note, we worked with a developer to build the website, so my team did not have a hand in customizing the files. Any insights are greatly appreciated.