Our customer has an op-premise AD synchronized with Azure AD via Azure AD Connect. He also have an hybrid Exchange 2016 environment. He doesn't have other on-premise server. He has 100 users with M365 business standard license.
Now he wants to join all the 100 users PC from on-premise AD to Azure AD, and then he wants to decommission the on-premise Domain Controller and Exchange Server. Basically, he wants no more on-premise server and uses only Azure AD.
I have little questions: 1- Does he need to buy an Azure Active Directory Premium P1 plan for all the 100 users? Or does he only need to buy 1 Azure AD Premium P1 license to activate the Azure AD joining function? 2- How can we decommission the DCs and Exchange after all the pcs have been joined to Azure AD? Can we simply poweroff the server or are there some activities to clean the M365 tenant? 3- Will on-premised synchronized users in Azure AD remain after the DCs and Exchange decommissioning?