The process required to restore an Exchange Offline Address Book (OAB) server is similar to the procedure you would follow to recover a public folder or mailbox server: without touching any objects in Active Directory, perform a recovery according to the instructions provided in Exchange Server 2007 Disaster Recovery.

Essentially, you will rebuild server using the same name, reinstall Exchange using 'setup /m:RecoverServer', and then restore the public folder database from the most recent backup.