Are you receiving a sickness or unemployment benefit? Or are you receiving a statutory pension, but are you also employed in the Netherlands? Then you are still an employee and remain insured in the Netherlands. You are therefore not entitled to an S1/121 if you emigrate.
Are you receiving a Dutch statutory pension, but do you also intend to work in your new country of residence? Then you are not entitled to a S1/121. You need to arrange health insurance in your country of residence.