Awoke this morning to a scary site - the screen was black. Then I noticed the charging indicator light was orange. I turned it on, and the phone booted as if nothing bad had ever happened. It was only 75% charged.
I'm guessing maybe the Fastboot screen may have a 24 hour timer (in which case why only 75% charged 5 hours later?), or maybe the thermostat in the wall charger turned it off and the battery power eventually died (but then what caused the wall charger to start charging again?).
So now I know I need to be sure to see the phone in both Windows Explorer and on the SDK screen before starting the Fastboot process.
But for the future reference of myself and others who may read this, I'm still wondering:
2. If I had simply pulled the battery, would there be any risk of bricking, or would it have simply returned to normal like this morning?
3. Could selecting any of the options on the phone (Fastboot, Recovery, Clear Storage, Simlock) have helped me without a functioning USB connection?