Hi,
The fact that it removed the 8 previous variants is normal.
This is a feature so that you can not only add new variants but also remove the ones you don't want anymore through the import system.
Regarding the images, that's normal that you lost them too. When a product or a variant is deleted, the system checks that for each image attached to it, it is not attached to another product/variant and if that's the case, it deletes the image.
This is so that the upload folder where the images are stored does not get exessively big with lot of images being there while not being used. It's possible to change that behavior thanks to a hidden setting, by adding an entry with the namekey "keep_category_product_images" and the value "1" in the hikashop_config table through your phpmyadmin.