This is a tricky question and open to interpretation by individual enforcement officers. First, you've acknowledged that it is illegal to keep the smallmouth bass. If a bass is bleeding from the gills but still alive, if you can remove the hook without doing anymore damage - do so and release the fish. If you will do more damage to the fish or gills by removing the hook, clip your line as near the hook as possible and release the fish.
Even though the fish is bleeding, there is still a chance it will survive if you release it back into the water. Even if it doesn't survive, the fish is not being wasted because it will probably be feeding some other species of fish or wildlife.
If you encounter an officer in the field during the described situation, be honest with him and explain your rationale behind the decision you made in whether to release the fish or any other alternative. Our officers understand these things sometimes happen when fishing.