The use of the phrase "reasonable accommodations" tends to indicate you are actually asking a legal question, rather than a personal or practical one, in spite of saying that you aren't looking for legal advice.
Still, consider a few of these possibilities.
You could choose to say "We want you to take a company-paid sabbatical. First help us train someone who can replace you temporarily. Then, we will pay you to get your depression under control, and come back to us in better shape to resume your prior work."
You could choose to say to this employee "We will let you take as much time off as you feel is needed. Just work hard when you can and tell us when you can't. We will help you in any way we can, both professionally, and financially. Somehow, we'll deal with your work when you aren't here."
You could choose to say "The specifics of your role simply cannot accommodate as much time off as you seem to need right now. So, we are bringing in a replacement to fill your unique role. You will be moved to a different, less unique position. But you will retain all your current pay and benefits."
Any of those could be considered "reasonable" from a humanistic perspective.
You could also take a more drastic path.
You could choose to say "We are sorry, but the unique role you play in our small company demands someone able to fill it on a full-time basis. Based solely on your performance, we need you to find another job. We'll give you a generous severance package, great recommendations, and help you in your search for a job which isn't as demanding of your time."
You could choose to say "In fairness to the company, you aren't currently in a position to fill this role on a full-time basis, as indicated by your frequent absences. We are willing to let you reduce your role to part-time, and share the role with another part-timer until you are able to resume full-time work. If you aren't willing to compromise on that, we'll have to ask you to leave."
Aside from the legal ramifications, you need to consider the employee's needs, and value, and you need to consider the company's needs. What is "reasonable" is different in the eyes of the law, in the eyes of a depressed employee, and in the eyes of someone responsible for the needs of a business.