It is in. You already fight against Necromancers.
But the player himself will never wield magic. The nearest he gets to using magic will be in using rare artefacts which may inhabit certain effects. But no flying fireballs and such things.
"I am a Paladin!"
>OMG, Malthus, there are no damn paladins in Battle Brothers...<
"OK, OK! Then I´m a wrecked down minstrel drunkard pretending to be a paladin, singing so wrong in the midst of battle that even the undead run in fear... Better?!"