[css-cascade-7] For multiple named @sheet imports, what happens if not all sheets are present?

[KurtCattiSchmidt]

@romainmenke raised a great question in the @sheet draft I have in review (#11980 (comment))

@import one, two from url('foo.css') where 'foo.css':

@sheet one {}

Does it fail entirely, or does it still import one?

My weak preference is to still import one, but I'm curious what other thoughts are.