First thing to consider is wether Payroll Checks were issued (or Bank Transfer was done).
If it was, re-executing Payroll Calculation for the same period for an employee (or all employees) could generate a claim or a second payment if there was a change in Master Data.
If it was not, then you should be able to delete the Payroll Cluster Results of the "No Show" employees using t-code pu01, delete their Time Evaluation Cluster Results using program RPUP2D10, and then delete the employees.
Note that you can execute Payroll Calculation many times as long as the Payroll Checks or Bank Transfers are not generated.