If you delete your account, all of your remaining SG balance which you have not decided to "Sell to the market" or to "Sell to us with a guaranteed value," will be deleted.
Please be careful when deleting your account, because once deleted, the balance cannot be returned.
*For details on how to sell the SG you have earned with cashback, see the article here (How can I sell the SG I got through cashback?).