If a close relative who is registered in the Non-residents Records Database (RNI) dies, contact the National Office for Identity Data (RvIG).
(Information in Dutch)
The RvIG can check which public sector organisations the deceased person had dealings with. Based on the results you will be advised as to what to do next.
No death certificate
To report a death you usually need a death certificate. If you don’t have one, you should request a death certificate from the local authorities in the country where your relative died. The local Dutch embassy or consulate in that country may be able to help you with this.