When you leave the Netherlands permanently you need to deregister yourself from the municipality (the Basic Registration of Persons (abbreviated as: ‘BRP’)) where you are staying. This deregistration can only be done as of 5 days before you actually leave the Netherlands. Note that this regards 5 days, not working days, and therefore includes Saturday, Sunday and Holidays. Next to deregistering, you will need to send the residence permit back to the Immigration and Naturalization services (IND) as the residence permit (the card) remains property of the Dutch State.
Next to leaving the Netherlands permanently you officially also are obliged to deregister yourself from the Dutch BRP if you would leave the Netherlands for a longer duration than 8 out of 12 months. Do take into account, that if you are a holder of a Dutch residence permit, deregistering from the BRP would result in the revocation of your residence permit by the IND as being registered in the BRP and thus having your main residence in the Netherlands is a requirement to keep your residence permit.
For more information about deregistration from the municipality of Eindhoven, check with the website of the municipality of Eindhoven. (There is a translate button at the top of the page.)