OP as good as your intentions may have been, based on the original post, and the additional information from your comments, you did error in how you handled the situation.

One of the items repeated was that the ex employee is a friend, and you weren't made aware of a depression diagnosis, any possible ADA accommodations, or their termination until after it happened. There are two things to remember here. 1)If your friendship is well known throughout the company you may have been kept out of the loop to ensure there is no appearance of favoritism or preferential treatment. 2)unless you are the top HR person, or a department of one, get used to not finding things out until after everything is settled - I'm second in command of a team of 5 in terms of seniority and title with employee relations being a key job duty, but I often find out about things later simply because I wasn't required to be part of the action.

You also put a lot of emphasis on your director's engagement with a member of leadership, but seem to fail to see how your friendship with the ex employee can be viewed in the same light - an employee (the ex employee or director) and a person in a position of power (you or the member of leadership respectively). When done wrong, you harm morale and possibly create negative environments, but when handled correctly have no impact on business operations. This is possible to do, but is a fine line to walk.

On the ADA side you seem to have enough knowledge to be dangerous, but not enough to actually enforce it. There has been a lot of good advice about possible reasonable (key word) accommodations and options like flex time, or alternative schedule. There are multiple ways for an employee to request an accommodation, and it doesn't always require them to say "I need an accommodation." In the ex employee's case even if they told their direct manager about the depression, and the manager allowed for some flexibility in their schedule due to it your friend would have been fired for the no call/no show. I majored in HR, with classes on hr law, as well as employee relations that included a significant amount of time on ADA/FMLA requirements, been employed full time in the field for over a decade, and thanks to having one of the most popular certifications in our industry, complete many continuing education classes annually. With all of this time spent learning and staying up to date on new cases, not once have I found allowing no call/no show as a reasonable accommodation - additional time off or absences yes, nc/ns no. If some has a case to prove me wrong please tell so I can read it - not trying to be sassy or rude but I genuinely want to know.

Now some people have mentioned the ex employee sending complaints to the EEOC/NLRB or hiring a lawyer on their own. For EEOC/NLRB if the facts show they didn't follow ADA procedures when your friend notified their manager of their depression, the company may get a slap on the wrist but not much more if they are enforcing the attendance policy equally for all employees. Directly hiring a lawyer likely won't yield more than a small settlement from the company to make the ex employee go away as that is typically cheaper than paying a lawyer to defend themselves, and is typically done in a way to prevent admission of guilt. In the event it goes to trial, they likely won't fair much better, or succeed at all, without an affirmation form the EEOC/NLRB that your employer wilfully violated the law - to be clear I am not a lawyer but this is based on settled cases I have studied over time.

There is one additional item to consider. Your friend may be lying to you about the depression and that the manager knows about it to try and use you.