If you unplug the e stepper the controller will not notice (while off or you will damage the stepper driver)
Also if you remove the E stepper driver the controller will not notice that either. (Also while off)
Both will disable E extruder stepper
Re that thermistor, I just wire a 100K resistor over the thermistor inputs. The printer then thinks its 25c all the time.
Its quite hard to remove temperature stuff from firmware, especially if you have a LCD (Last time I looked)