If the question is: Can he win a game or two if necessary to keep us in the playoff picture or even win a playoff game...
There's no way to answer that until this team has better talent. If we have a defense that can keep playoff-level teams to less than 20 points, and Boyle can score 21+ points against a playoff caliber defense, even if it doesn't look pretty, then yes. But, we're not at that point yet, where we can actually answer that question....
Everyone else above covered the other issues surrounding the backup QB...