It's theoretically possible to go infinite if you never scare villagers, but that's pretty hard! Our quick playtesting got to 19 villagers eaten but we think higher is possible with more time!
Technical notes: When you eat a villager, one soldier spawns. Any scared villagers run back to town and spawn both a soldier and regular villager. Existing soldier's speed increases every two villagers eaten and new soldier's speed scales with total soldiers in play.