I think it can be done!
I decided yesterday to do the Rocky Raccoon 50 miler in Feb. in Texas.
I still have a small fracture in my hip-going to start aqua jogging this week.
I haven't run in 3 weeks, and then my longest was 10 miles(and i hadn't run in about 4 months until I fractured the elbow).
I know I am lucky, I can plod along at a 10 min mile for a long time. I can not run for a year and then go do a 10 miler.

We will see how doing a 50 mile run in 3 months from now turns out!