Run Jono - I'd start off with some 50s. They're manageable and usually always in daylight. It's a good round distance and unlikely to cause damage. Anybody who has done long distances will tell you that something funny happens about the mile 65 point - beyond that is the running equivalent to the 'death zone' where things start breaking down. Only very special people can keep running, or even keep going, for 100+ miles.
I'm still around but not doing much running. Went out today in the forest near me with Archie - 5-hr run.
Came to one of my usual paths and found that someone had turned it into a mountain bike trail. A sign said something to the effect that this new route was now open and anyone using it should take 'this extreme downhill course very cautiously until you are used to it.'
I don't remember needing caution in the past so I set off down it at a good pace.
Man! What an experience!! You're in this kind of chute thing - impossible to get out of, stop, or even slow down! Occasional leaps into thin air, big swooping hairpins, rocks and tree roots. I found myself yelling and laughing out loud involuntarily.
Don't know what Archie was thinking - he came a different way down. Got more sense.
Got the bottom still laughing, breathless, and completely exhilarated out.
A great tonic. Fortunately I didn't meet any bikes which might not have been so good.
Can take a long while to heal. I had AT in one foot and it took 15 months before it cleared up to the extent that I have forgotten I had it. Now completely healed with no hint of re-occurrence - 2 1/2 years now. No lumps/bumps to see, either.
I got to this stage through careful management and excellent service from a sports injury therapist doing regular deep tissue massage.
You are not more prone to have it happen again (unless you repeat any mistakes that might have caused it in the first place).
I'd continue with heel drops and calf stretches as good preventive medicine, take care with shoe purchases to not choose models that aggravate the tendon (look for a low back).
For your first runs take it very steady - no speedwork or downhills. Find a flat, smooth surface and see how you get on. If the pain is very acute or sharp you should stop but if only dull throbbing persevere - you will find it will ease off after a few miles. If it comes back later on in the run that's about the time to stop.