I think the settlement is not to screw Richards over any more than what has happened so far.
There is enough general information out there that the issue may in fact be a border entry ban or a loss of a work visa. A simple search with the keywords will find literally dozens of immigration attorneys that say people who even just admit to controlled substance possession/use even from decades ago can be potentially banned from entry or lose their work visa.
Nigella Lawson admitted cocaine use. Lost her work visa for a year and had to do her US based tv show via satellite from Britain. She had no drug convictions, no charges, not even an arrest.
Amy Winehouse lost her work visa for a year over plea to marijuana possession in Norway. She missed the 2008 Grammy's where she won 5 Grammy awards and was nominated for a sixth. Pot issues are specifically treated more leniently under the entry ban and work visa revocation statutes.
Kate Moss had a photo in the tabloids of her apparently using coke. Lost her work visa. No conviction, no charges, not even an arrest. She's been trying for a visa ever since. She even got into a heated discussion with the US ambassador. It's been 10 years.... and she still can't get a visa.
It's even spelled out on the official state department website that this can happen.
http://travel.state.gov/content/visas/en/general/ineligibilities.html#Ineligibilities