This type of situation has come up in my group a long time ago. The Goal is to have enough difficulty to be a proper game without just giving reward away. I had written, and since lost it, an easy “random” type scenario for those who missed games. I took several pieces for other scenarios and mixed them together. It had a small story about a lost item which was hidden in area/building (within 2x2 foot area in the center of the table), which had a reward to retrieve. Kind of like the Treasure Hunter scenario, where you have to search buildings. The reward, I think, was a Shard or 2d6 gold, or something. The random part was the monsters and creatures in the way. These would be played and controlled by other players. This is the fun part. I had a random D6 chart similar to this: (These creatures would be placed randomly on the field before Warband player deploys) Roll D3+1 times on this Chart
1- Zombies: 2D3 Zombies, these zombies just move around randomly, use scatter die. Until they can charge. BRAINS!
2- Wild Dog Pack: 2D3 Wardogs, They’re fierce and hungry. Use scatter die the move randomly. The dogs are hunting for food and will not be more than 6 inches away from each other as the move
3- Chaos spawn: 2D3 Chaos Spawn. Use normal rules for these.
4- Monster Hunt Creature: Randomly roll which Monster is in the area/table. This monster has no Horde as it is young and still looking to make one. Use scatter die to move as its searching for treasure. OR Thing in the Ruins! (Use Thing in the Woods Model) Use rules as normal. It’s hungry and looking for food. It’ll eat anything alive with in Charge range, (including other creatures on this list, except Zombies) Roll Odd or Even to determine which.
5- Possessed!: (this is fun) make a Possessed Model. Roll D3 Mutations and Randomize the Mutation’s Chart. Then roll 4 experience advancements, re-roll “New Skill” He’s to crazed to learn skills. Use a scatter die to move 2d6 up to it’s max movement. He will charge as normal. If any aggressive action is taken towards the Possessed he will run towards the aggressor until he can attack the aggressor or any Warband member within charge range along the way. Meaning, if he was shot at, he will move towards that shooter.
6- RATS!: 3D6 Giants Rats. They’re fierce and hungry. Use scatter die the move randomly. The Rats are hunting for food and will not be more than 6 inches away from each other as the move. The rats are worth ˝ XP per kill.
This is just an Idea, not any hard and fast rules. This can be modified to suit your needs. The point of it is to have 1 player who missed a game(s), and another play NPCs that another player could play without have to spend the time making another Warband just for one game.