Basically the device isn’t seen by the sandisk firmware updater for windows right? Does the drive ever appear where you could drop another HEX file on it? You don’t have an SD card in the device do you?
If you can’t access the device and it won’t properly initialize in windows it does sound like it is in limp mode so you could basically drop chinese firmware on the device then bring the device back using sandisk firmware as described on the wordpress blog I created. Several post down you will find a topic with BOP in the title. The link is in that post.
This method would work as the .bin file would still be able to load using the updater program where as you can’t do a .hex update without a windows update or device access to do so. All files you need are on the site.
