You'll have to mod the game, you have two methods of making the heroes die like soldiers:
1) In each character ODF file, add FleeLikeAHero = 0
or
2) In each mission script, after ScriptPostLoad() add this command and repeat the command for each ODF class name
SetClassProperty("rep_inf_example_trooper_name", "FleeLikeAHero", "0")
1) In each character ODF file, add FleeLikeAHero = 0
or
2) In each mission script, after ScriptPostLoad() add this command and repeat the command for each ODF class name
SetClassProperty("rep_inf_example_trooper_name", "FleeLikeAHero", "0")