Actually, you could likely go many generations using the same rooster. Line breeding indeed. However, if this rooster isn't all that, doesn't throw great offspring, you'd need to swap him out ASAP, or at least I would. If he does throw some great looking/producing hens, keep him. But, cull, cull, cull the duds. This is what has to be done. Hope that helps.
We had a GREAT looking Speckled Sussex roo, I mean a looker. Unfortunately, he never passed that on to offspring. All them were quite poor examples and weak layers. It happens. Had to make a change. Conversely, we have an older Barred Rock roo who just flat throws great chicks. We'll miss him when he's gone.