Is it ethical? I wouldn't say so, but I do think that is the economic argument.
They locked the owners out of their devices, hence the bounty from Rossmann to "hack" them. They gave one option, but took one away.
> I think the answer to 1 is "yes". They wouldn't have bought the asset if they couldn't extort their customers.
It's definitely how the law is currently being applied, and they probably won't have legal trouble from it, but I argue this is a corruption of ownership law, and any kind of update that is against the device owner's wishes (that they are deliberately prevented from reverting) is equivalent to criminal hacking. I can't emphasize this enough - the devices in question do not belong to them. They sold them, these are privately-owned computers they are interfering with.
Especially in the case of bankruptcy - the device owners have no more of a business relationship with this new owner, than they do with a random hacker making printers emit goatse.