Originally Posted By: seanog
If I plugged the cable back in with the machine running would it cause a disaster?.
If not how could I reformat the HD?
I'm not sure what stage you're at right now. If it boots from the USB was the HD still connected? If so you can re-partition it booted from the USB per my instructions above.

I wouldn't recommend hot-swapping cables. You'd need to remove the HD and put it into an external case. It's a bit of a pain for sure but if it was my machine I wouldn't risk hot-swapping.