The Chicago marathon was a week ago, so what are your plans for the rest of this year and next year? You have just trained for 18 weeks and are possibly in the best shape of you life why stop now? There are plenty of races between now and the end of the year. Try a local 5 or a 10 K race. Yes I know you are a marathoner so while would you run "just" a 5 or 10K race? Why not? Enjoy yourself, enjoy the neighborhood and the other people running. My family has a family tradition of going for a run on Thanksgiving morning. Of course no one runs with me but I try every year. Maybe this year. The point is slow down run short and maybe your family will run with you someday.
After finishing the marathon a lot of people cross it off their bucket list. Again what a waste. Now that you can climb down the stairs going forward and you can look at your shoes and think of going for a run, it is never too early to think about next year. Hopefully you have found some new friends who also enjoy running. Give one of them a call and arrange a time and place to get together. If you keep running during the winter you will maintain some level of fitness. After the first of the year begin looking for some races and start training for them.
After a few races you will begin thinkging about the marathon again!
Resist the urge of being a one and done. Sign up for a marathon in 2012. Maybe if you are a charity runner for AHA you get to read my emails again next year. Now that is really something to look forward to. Best of luck, see you next year.