"Marcos was deceptive and it led to his demise." is grammatical, though "this" in place of "it" sounds a little better. The antecedent of "it" or "this" is the preceding sentence "Marcos was deceptive". This sort of anaphoric construction is unusual, since the antecedent and pronoun have different grammatical categories ("parts of speech"). The antecedent is a sentence, while the pronoun is a noun phrase.
If the antecedent is substituted for the pronoun, we get the ungrammatical
*[Marcos was deceptive] led to his demise.
which is ungrammatical because a sentence cannot occupy the position of a noun phrase. However, if the sentence is nominalized, it's much better:
?"That Marcos was deceptive led to his demise."
"Marcos' being deceptive led to his demise."