Again, IANAL, but according to 17.1.b, the data subject..shall have the right to obtain from the controller the erasure of personal data concerning him or her .

Again, IANAL, but according to 17.1.b, the data subject..shall have the right to obtain from the controller the erasure of personal data concerning him or her ... where one of the following grounds applies: (17.1.b) the data subject withdraws consent on which the processing is based 17.1.b appears to be the trump card held by the data subject. They can withdraw consent at any time and request erasure. Once they do, the data controller can then use any of the exceptions in 17.3 to deny them. However none of these is "because I want to keep records of all firings". My further understanding is that you certainly could keep a record that someone was fired, just not a record that included any personal information that could identify who that was. i.e. pseudonymization..