My mouse uses a WebUSB app to configure stuff. I just downloaded all the files that it uses, and now I can use it offline.
> and can be reverse engineered long after its manufacturer has dropped support or gone under
Nothing really stops you from reverse-engineering a WebUSB app either.
The question is if users will consistently have the foresight to archive such web apps, especially if the manufacturer has set up their bots.txt such that The Internet Archive skips it.
Traditional programs are incedentally archived by nature of having to be downloaded. They sit in downloads folders, old backups, thumb drives, etc.