If only descriptor file is delete you can recreate it using below kb
if corrosponding delta.vmdk is also deleted you may have to point the VM to next available delta file if there were multiple snapshot or point it to base disk "flat file"
For vm with multiple snapshot you may check complete chain consistency using command:
vmkfstools -e filename.vmdk
vmkfstools -q -v10 "your_disk.vmdk"
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