Outlook has never been a requirement for work, you can very easily use any email client or outlook.com web app. Outlook is arguably the easiest to replace.
Excel is the only thing holding Office 365 together.
Word, Outlook, OneDrive, Teams, SharePoint are all very easy to replace
Every organisation I've ever worked in, as an employee and a consultant, has used Outlook for email, meeting scheduling, and room booking, and the underlying Active Directory that manages employee logins, permissions, and how it all links to (Windows) device compliance via GPO.
And if the decision away from Windows is an indicator, they will likely be moving email clients as well