How it's possible to recover vmdk file from flat file in ESX?

There is another way:

SSH the ESX Server then Do As :

1-   # cd /vmfs/volumes/myvmfsvolume/mydir

2-   # ls -l XXX-flat.vmdk ==> Write down the size of the file

3-   # vmkfstools -c (Size of the file) -d thin -a lsilogic temp2.vmdk

4-   there are2 new files created:  temp2.vmdk and temp2-flat.vmdk are created as a result

5-   # rm temp2-flat.vmdk

6-   # mv temp2.vmdk XXX.vmdk

7-  Edit the descriptor file (the XXX.vmdk)==> Simply right Click and Edit then Find the "RW    ####### " and replace temp2.vmdk to XXX.vmdk

8-  Power Up the VM

Dear Khaled thanks for your Notice

As you know, when you remove a VM or a vmdk disk from disk (and not only from inventory or VM) you loose all your data.

Is possible to roll back? Yes... just restore from a backup. 

But if you do not have a VM backup? Or a recent one?

The solution could be the VMDK Recovery Tool.