If an employee has been malicious during their tenure then other systems should have detected and caught that. That scenario can be decoupled from the termination scenario.

Think about making a 2x2 matrix (nod to Pascal’s wager):

Across the top: fire immediately, don’t fire immediately.

Down the side: employee is benign, employee is malicious.

There’s only one square where the company is at risk- bottom right.

The algebra is easy: terminate immediately and the company is not at risk.