Mark missing blocks in the admin panel as not available instead of showing a blank page

[lorenzrabs]

Hi guys,

i just renamed one of my blocks that was used on a page. i noticed that you get a blank screen if you wanna navigate to the page in the admin panel.
After looking into the docs i found "ERROR: Block with type "teaser" was found in block data, but no block with that type is defined in the config for field with schema path pages.layout."

I think it would be cool if the page inside the admin panel would load normally and on the specific block it just displays an error, that the block is not available. Maybe even offer the option to delete the missing block.