For me and for those that I write training plans for, I recommend 2 weeks off after an "A" marathon. My rule of thumb is a day off/easy pacing for every 3k of racing. So a 42k (marathon) race would be 14 days of off/easy. Almost all, I schedule for 2 weeks off. Then, I schedule a reverse taper. So look back at the mileage from prior to the marathon. I do about 30-40% of the peak in the first week back, then 50-60% in the second week back, and around 75% in the third week back. The first and second week back to running are kept completely easy. The third week back is the first week with a hard workout. From there, I restart the training with likely new training paces based on a new assessment of current fitness.
Summary:
Week of 9/10/18 - Marathon Week
9/17/18 - 1st week off
9/24/18 - 2nd week off
10/1/18 - Return to running at 30-40% of peak mileage for total of week (i.e 50 miles peak mileage in last plan would call for 15-20 miles in this week). All paces kept easy (or ~12% slower than marathon pace or slower).
10/8/18 - 50-60% of peak mileage. All paces kept easy (or ~12% slower than marathon pace or slower).
10/15/18 - 75% of peak mileage and first hard paced workout. Resume marathon training.
From 10/15/18 to 1/7/19 is 13 weeks of training. So plenty of time for another good marathon training cycle.
From there, the long runs progressively build back up to the peak. Since the training period of 13 weeks is slightly less than a normal timeframe, I usually only hit peak mileage once. I believe that if one hits peak long run mileage too soon in the plan that the training load will stagnate and you'll stop adapting to training. Then, you'll end up maintaining and possibly burning out. So I don't recommend starting the long runs up too high after coming off a previously completed max long runs (back in early Sept). Save those maxes for mid/late December.
Here's a post I wrote about my own ability to recover from a marathon and how long it usually takes (
How long does it take for me to recover from a marathon?).
Hope this helps!