"Shut down after burn", another remarkable solution in search of a problem. This may have made sense with 1x, 2x, or even 4x burners. After that, its utility becomes rather marginal with the latest burners finishing a disc in about 2Â½ minutes. I suspect it was removed from the Burn dialog as a default due to its general lack of utility.
Editorials aside, if you really want this option go to File | Preferences | General and check "Show option to shut down the PC after burning".