Patch the tube, it might last for a couple more hundred miles however if those hundred are all at once or will take you to a far corner where the tire failure would ruin a ride replace early. I generally run tires until I have cords showing in two spots or they would ruin a long ride if they were to fail. I never rotate, rear tires simply do not last long enough to be worth the effort to rotate a half or nearly half worn tire. Buy tires in sets, replace the rear when due. Upon replacing the rear a second time replace the set and use the front for a trainer tire until it is totally gone. Doing this has given me a stack of trainer tires.