Both are correct.
The word no can be replaced in some contexts by none, negative, zero, or nothing.
He is a pronoun. The only synonym it has is to use the name of the person it refers to, i.e., "He is short." "John is short."
Normally one would not use, or need to use another word. However, if your sentence is "God is." then the alternative would be "God exists."
Reply is a synonym to answer. respond; response; result; do