The correct answer is C) localized overheating of the water drum. When a boiler tube bank baffle carries away or burns through, it disrupts the proper flow of hot gases through the boiler. This can lead to localized areas of higher heat concentration, resulting in overheating of the water drum. The water drum is a critical component that helps maintain proper water circulation and level within the boiler, so its overheating can be problematic. The other options are incorrect because: A) fireside burning of boiler tubes is a separate issue not directly caused by a baffle failure, B) excessive gas turbulence is a symptom rather than the primary effect, and D) incomplete combustion is not necessarily a direct result of a baffle failure.