How to fix Azure Active Directory?

A Client had their server stop working. the information was not recoverable and there was no backup. So a new server was purchased and they set up a new domain. All of the assets (about 15) were removed from the old domain and joined to the new domain (same name). They set up new ID's for the users and had them log into the domain. The previous set up was a hybrid set up, which is what the customer wanted. So now they have everything set up, however things are not syncing between on premises and AAD. I assume this is because of a mis-match on the user ID's and all of the old assets are in the Devices tab in AAD. The previous server was set up to sync between AD and AAD, however that is now lost.

So is there a way to fix this? I understand that the sync is not working because the user id will have a different SID than the new ones. Is there a way to delete everything in Azure an start over, however that is also a problem as email is attached to that. Really lost as to how I can help here.