After 2.5 months of rest, my hips are getting better. I'm going to try to come back progressively to exercice. The plan includes the 3 following stages:
  1. Come back to a decent shape - February
  2. Increase my VO2Max speed - March, April
  3. Endurance training and mountain trail conditions - June, July, August
Slightly more detailed plan:
  1. Come back to a decent shape - February
    Although I have rather good feelings while swimming, I'm clearly not at the top of my fitness anymore. During this stage I will try to remind my body what exercising means. I'll mainly stick to swimming sessions. I'll increase the distance to reach 2km, three times a week. Half of it will be Mommas-like training: typically 10x50m with 15s rest in between, or 100m 4-strokes (butterfly, back crawl, breast & front crawl). If everything goes fine I may try to come back to running (gently) at the end of February. I will keep very careful during this period, to listen my body in order to avoid being hurt again.
  2. Increase my VO2Max speed - March, April
    I'll then progressively go for a marathon-like training. I'll try to run two speed training a week to increase my VO2Max speed by doing 5x1000m sessions for example. I'll also add a gentle endurance run (2h) on the week-ends. I will keep one or two swimming sessions per week. If everything is fine, I may then run a marathon at the end of this stage (as a short term objective) but without reaching a destructive hypoglycemia+dehydration state like in Amsterdam last year.
  3. Endurance training and mountain trail conditions - June, July, August
    The really enjoyable training will start from June :) . I'll do my best to leave Hyde Park at least for Richmond Park. I plan to run a couple of times on the South Coast (the Downs), where the succession of small hills can provide an excellent playground for my training. Two long sessions in the Lake District or in the North Wales will be necessary for proper ascent and technical terrain training. A week hiking in the Alps (or other mountains) in July would be perfect. Then slowing down up to the end of August to be fresh for the UTMB.
The two main issues that may arise will be the injuries and the boredom. I'll stick to a week of rest every month. Optionally, I'm still considering to buy another bike, maybe second hand this time. I'll replace long running sessions by cycling to rest my knees, hips and lower back.

Ultra hard to follow.