Again, I’ll ditto Zeke. Ankles are interesting. 6 years ago, right about this time of the year, I was running on a paved trail near a river that had flooded. I was running through shin deep water when I hit a pothole. I didn’t brace for it at all and my ankle took the full force as I went down in a heap. I couldn’t even stand on it for a few minutes and I had to walk for a while before very gingerly jogging back to where I parked. Later that evening, I couldn’t put any weight on that foot. I was sure I did severe damage. The next day, same thing. The day after, it was feeling quite a bit better and tried to run. I made it about 2 steps before stopping. The following day, I was very cautiously running and I was back to normal within a week.
As for training suggestions, I’d suggest trying to mimic your planned running schedule by time and effort as much as possible. If you had a 20 miler at 8:00/mile planned, try doing something or a combination of exercises for 2:40. If you had 800s at 3:30 planned, try 3:30 pool running or cycling repeats.
Again, hopefully you’ll bounce back quickly and this will be something you laugh at worrying about so much by the time Boston rolls around. If not, focus on your health first because that’s what is really most important.