Spinoza's view is that there is only one substance, and nothing but one substance, which can be alternatively referred to as 'God' or 'Nature'. Your quote, with its hypothetical 'if', does not conflict with this view.
The following passage sets out Spinoza's pantheism. It departs a bit from your language but does, I think, accurately answer your question :
Pantheism..., being a term derived from two Greek words signifying "all" and
"God," suggests to a certain extent its own meaning. Thus, if Atheism be taken to
mean a denial of the being of God, Pantheism is its extreme opposite; because Pantheism
declares that there is nothing but God. This, however, needs explanation. For no
Pantheist has ever held that everything is God, any more than a teacher of physiology,
in enforcing on his students the unity of the human organism, would insist that every
toe and finger is the man. But such a teacher, at least in these days, would almost
certainly warn his pupils against the notion that the man can be really divided into
limbs, or organs, or faculties, or even into soul and body. Indeed, he might without
affectation adopt the language of a much controverted creed, so far as to pronounce
that "the reasonable soul and flesh is one man" - "one altogether." In this view, the
man is the unity of all organs and faculties. But it does not in the least follow that
any of these organs or faculties, or even a selection of them, is the man.
If I apply this analogy to an explanation of the above definition of Pantheism as the
theory that there is nothing but God, it must not be supposed that I regard the
parallelism as perfect. ... For Pantheism does not regard man, or any
organism, as a true unity. In the view of Pantheism the only real unity [complete, authentic, unqualified substance: GT] is God. But
without any inconsistency I may avail myself of common impressions to correct a
common misimpression. Thus, those who hold that the reasonable soul and flesh is
one man - one altogether - but at the same time deny that the toe or the finger, or
the stomach or the heart, is the man, are bound in consistency to recognize that if
Pantheism affirms God to be All in All, it does not follow that Pantheism must hold
a man, or a tree, or a tiger to be God. (J. Allanson Picton, 'Pantheism: Soime Preliminary Observatons', New England Review (1990-), Vol. 24, No. 1 (Winter, 2003), pp. 224-227: 225.)
There is nothing to contradict Ethics, I, Prop.5: 'There cannot exist in the universe two or more substances of the same nature, i.e. of the same attributes.' Since there is only one substance, which possesses all attributes (though thought and extension are the only ones known to us) there are not and cannot be two such substances.
The 'whole reality' is God; there is nothing but God. There is not God + the modes. The modes are not ontologically dependent on God. 'By mode I understand the affections of substance (substantiae affectiones)' (I.Def.5). The modes are 'affections ... of the attributes of God [as substance: GT], by which the attributes of God are expressed in a certain and determinate way' (I.Prop.25, Coroll.). So, for instance, the attributes of thought and extension are expressed in a particular, 'certain and determinate' human being. A mode is typing this.
J. Allanson Picton, 'Pantheism: Soime Preliminary Observations', New England Review (1990-), Vol. 24, No. 1 (Winter, 2003), pp. 224-227.
Spinoza, Ethics, tr. G.H.R. Parkinson, Oxford: OUP, 2000.