Why did iCloud delete my inbox and sent emails when I was forced to disconnect from ICloud

After my recent uograde to 10.9 I couldn't connect to iCloud as I needed to change my Apple ID to another email address ID - when I disconnected/reconnected to iCloud it deleted all the emails in my Inbox and Sent folder - complete disaster as some of these emails where critical to my business. Is it possible to recover these emails? More importantly why does Apple wilfully allow their software to delete a customers data that isn't on the cloud?