Thank you for asking this question on the **Microsoft Q&A Platform. **
If you disable a user on-premises will be still synchronizing to Azure, but it won't be able to log in.
If you what that the user to disappear from your Azure AD, you can:
- delete the user in your On-premises AD; or
- move the user to an OU that is not synchronizing to Azure AD
Hope this helps,
Carlos Solís Salazar
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