Remember also that the Martians bring 'humanoids' from Mars as their 'travelling larder', so a few survivors from this race could be running around, possibly desirable for capture as they understand basic Martian tech or the intell they could pass on prior to an attempt to take the war back to Mars by some countries (a la 'Edison's Conquest of Mars')?
Plus, joining the 'no zombies' idea, try to make it more VSF than Steampunk, like IHMN - which has design rules and character creation rules for just about anything Wells, Verne or anyone else pretty much ever thought of!