The problem that you see is that the new LUN is not the same as the old LUN. It will have a different signature, actual vs what's on the disk itself, so the LUN will not match what ESX is expeting, which is why the extent is not added back to the host itself.
If there is data you need to recover, you'll need to open an SR with vmware to see if they can get data off the LUN. You may be able to open that VMFS with a 3rd party tool that can ready vmfs, but if the LUN's don't match exactly, you won't be able to recover the "hole" in your existing datastore.
-KjB