Yup. Totally Normal. He can randomly die ruining your entire run. I think some kind of alternative path should open up when this happens where Schmedes (the ruler afterwards) could try to keep the Brigade together or to reform it into some kind of state. Either way, I think that the game should not simply end for you when he dies.

The brigade is supposed to be a bandit state that only exists on the back of Dirlewanger. If he dies, there's no way they could hold together. I do have to agree that the fact is death is unavoidable or undelayable for the player isn't that fun.

Then after his death something should happen. I don´t think that the remanents of the Brigade should exsist. Maybe the Ural League could invade to restore order? For me, the idea of the "corpse" of the Brigade still existing sounds kinda weird.