This is old post but still a steady pain for store owner with multiple storeviews. It is super annoying to need to check each storeview and each image. In our case store with 5+ Storeviews it just does not make fun...

How we fixed it?
We just fixed it for our clients by creating a module which syncs the image roles. This modul adds a "sync image" button which allows to sync all image roles with one click. Than you can just delete/replace images. And it has a "sync mode". This leads to automatically sync images after click on regular "save"

More information can be found here:
https://www.konvis.de/magento-2-multistore-tool-image-roles-fixing/