Can you confirm if you are uploading the CSV on the PRODUCTS or INVENTORY section of your admin? There are two separate CSV files that can be used in the admin. One for updating products and one for updating inventory. The product inventory CSV should not be overwriting product images.
You can confirm the steps for updating inventory through CSV on this page: Shopify Help Center | Exporting or importing inventory with a CSV file.
If you are importing and updating inventory using the steps provided in our Help Center but are still experiencing issues with the images disappearing, please reach out to our authenticated support team for further help with this.