THe dissipation discussion does draw us dangerously.
For me, the harder-to-understand issue is: how to get the voltage at the comparator's output pin lower than the Vbe(sat) of .65 volts of the 2N3904.
As an exercise, I tried to change the comparator to an LM211, to see if I could reproduce the calculations. There was no Vsat, on any LM211 manufacturer's datasheet. But I did find a V(OL), low-level output voltage, same 0.4V as the LM2903, optimal at 8 mA. Can I use this? In which case, the pulldown resistor would be 1450 (say 1.5K) ohms. Is this correct?