You cannot just change - first you will need to move the groups to your AD (create/add members). You must also ensure that users in the ldap are created in AD with the same ID - this may sound trivial - but in the real world this is very often not the case.
I really do not understand (beside removing an infrastructure component) why you would do this - there must have been a reason you chose ISDS in the first place.
Be aware - even though Windows AD is ldap based it is not a completely standard ldap server implementation - this may or may not have consequences in your situation.
HTH
Regards
Franz Wolfhagen
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