Within my free-writing I have stumbled across a roadblock.
My Sentence: "The concepts within a story should not be retained as mere memories; Instead, as ideas."
My Question: Is the semicolon used in the statement grammatically correct?
No, not at all. At best, your sentence might be "The concepts within a story should not be retained as mere memories, but (rather) as ideas." The semi-colon merely confuses an issue that was otherwise much more clear. Neither your “Sentence” nor your “Question” normally warrants a capital. What follows a colon warrants a capital only in a quote. What you might mean by “free-writing” or a “roadblock” I have no idea.