You should run again, don't worry, I am. However it is important to take the time to let it heal, and not do further damage.
You'll be surprised when the cast comes off, I was in one for four weeks and was shocked when I saw my leg, it was about 30 % smaller than the other one. Just muscle wastage. In addition I couldn't rotate my foot or move it back and forward, because the cast holds it in one position and the muscles waste as said.
It doesn't take long to build them up, I didn't have physio. But for a couple of weeks after the walking boot came off, which was on for two weeks after the cast came off) I was on crutches and when I walked my foot pointed the wrong way. Out to the side, and I had a pronounced limp. I was really worried and I recall my husband saying he thought I'd have to have it reset. I didn't. It was just the muscles.
As said for me, a month after the walking boot camp off I was walking normally and then a month after that I was running again.
The other thing you need to watch is if you damaged the tendons or cartilage when doing it. You won't necessarily know that until you're out of the boot. My consultant told me the exercise bike was good for it and then the cross trainer. However as a pp said. If it's not ready it will swell up and you'll feel it.
To put it into perspective when they x rayed me at four weeks they told me it was healing fine. But the consultant mentioned you can't see new bone growth on the x ray at that stage, it's too early and the bone isn't dense enough, but they knew it was there basically as something was holding the broken bits together.
If it's not dense enough to be seen on an X-ray, then it's no where near strong enough to run on.