The only supported method is to temporary disable dirsync, make the changes, enable it. If you don't care about the "supported" bit and don't mind taking a risk, you can delete the user in O365 first, then immediately recover it from the Recycle bin. This will in effect "disconnect" it from the sync process, and you should now be able to remove the on-premises user without affecting the cloud one. Again, this method is not supported, so use at your own risk.
Removing User in active Directory without messing up with Office 365
Yule Elben Junio
1
Reputation point
Hi there,
I would like to know if how do I remove a user in Azure Active Directory without compromising their Microsoft Office 365 Business license?