Send a VMFS header dump - maybe I can still find the lost flat.vmdk
If you want to attach the 3gb delta.vmdk to a newly created empty vmdk - create a new vmdk with exactly the same specs as the lost one.
Partition the new vmdk in exactly the same way as the old one. This really must be the same partition table as before !!!
If you want to try this - use a different datastore !