This is the time to think of maintaining the level of performance your body has reached as an athlete. The key to maintaining your level of fitness is a maintenance program while you contemplate a new goal.
For the 10K racer, keep your long run in the 8K range and use your new level of fitness to run some fast 5Ks. Your base training is in place, and you can use 5K races to improve your overall self-assurance and speed.
Half marathon runners can schedule a long run of 12K to maintain their endurance. The half marathon runner on the off weekends can schedule some 10K races to work on strength, speed and self-confidence.