Our previous AD controller is gone. Due to circumstances, we did not have backups and now we have installed a new one. Now, since earlier I did not have enough experience with Azure, I have a worry that if the program sees that there are no accounts on the controller, it will simply delete the previously created office365 services
Sorry for the delayed response. As you reinstalled a new AD, you basically have new identities (with new ObjectGUIDs) and the previous sync'ed accounts are now orphaned objects in Azure AD (not being managed from AD anymore). If you install AADConnect again it will not remove the existing sync'ed accounts from Azure AD BUT as it tries to sync all the accounts from your "new" AD, it will more likely cause many conflicts or duplicated accounts depending if the "new" accounts have the same UPN or ProxyAddress.