Q. Is this sentence correct, and if not, why? Because it is seriously injured, the dog may die.
A. The sentence is correct. Strict editors might say that it is not correct because the pronoun it comes before the noun that it refers to (dog), but they would have trouble finding such a rule in any authoritative grammar book. If someone has objected to your sentence, it is probably because they are thinking of the rule that main-clause pronouns can’t refer forward to subordinate clauses yet to come (“It died, because the dog was seriously injured”). It’s fine for subordinate-clause pronouns to refer forward to main-clause antecedents yet to come.