Hybrid exchange environment failed onsite server

[damienmurphy]

Hi, We have an Exchange hybrid environment where the onsite exchange server has failed and it not recoverable. All of the mailboxes have been migrated but are only partly manageable through the Office 365 portal. When you click on mail section of an Office 365 user it says it is only manageable from the Onsite Exchange. How can we remove the Hybrid setting and allow the users mail to be managed from the Online exchange and Office 365 portal

[#2]

You need to setup a new exchange server on premises to be able to manage these objects or if you are comfortable you can edit AD attributes of the mail enabled objects.
Or you can remove\disable directory synchronization altogether and make all objects cloud identities and then manage them online only.