As long as a victory seems sure, and the men have confidence in their general(s)/commanding officers, this might be very true. But once the battle odds turn bad, and those pro´s would see a horde of elephants charging their rear, i´m quite sure their thoughts would be like "that´s it..." ( same goes to a multiple ferocious charge of painted/naked dudes/cavalry while the pro´s have been weared down, trying to keep in formation, beeing on defensive ). Also, professional soldiers do not fight for glory, nor do they risk their lives if only to survive. They know when to duck, and to avoid dangers, no place for heroic deads, this guys fight for living, it´s their job, not their destiny. Elites, on the other side, would definetly fight to the end, no matter what, that´s why they are called so! Be it fanatism, devotion to lord/land/faith, be it their codex. Just my two cents ( been talking to some war veterans, this guys weren´t keen to throw their lives away, but to survive - if you don´t learn it, you won´t see the end of the fight/war.