It is very unlikely that you have done a taper bearing in by running it loose for 1/2 a mile. And for it to go wrong badly enough to damage the stub axle you wouldn't just have had a lot of play when you checked it after - you probably wouldn't have been able to turn the wheel by hand.
The worst case is you have a bit of pride, a £12 bill and a 4 mile walk to swallow tomorrow morning. That ain't that bad mate - I did it a few weeks ago for a starter motor.
Much more likely is that you have got away with it and we will see a post tomorrow afternoon saying you got it sorted.
And yes - thanks for the learn too - mine need doing at some point and I will def remember this...
