Just to keep everyone calm, I was only referring as DiapDealer said, to the File Open command (or drag and drop) not to Add Existing Files.
So of course Sigil would still be able to add html files - it wouldn't be too useful without it. It was just a question of whether Sigil should be able to open just .epub files, requiring you to use add existing to import html, css, images exactly as before.
But I think it'll probably remain for now as changing the code could be more trouble than its worth at this point.
Now, about dropping code view...