In the same way as you can change the way dynamic groups can contain non mail enabled accounts why can't we choose if a MU contains deprovisioned accounts.
It can be limiting that ARS effectively ignores deprovisioned accounts.
I have policies in place to help ( prevent ) the SD doing something they shouldn't like enable an account HR have marked as a leaver but once the account is deprovisioned these policies no longer work so the SD can enable an account.
Also I have teams who's only access is via the Managed Unit - if they deprovision a user account then it becomes invisible to them as it can no longer be a member of the Managed Unit. If my query for the MU includes a filter to locate deprovisioned users then ideally teh MU should display the users.