Allen was cornered by Katherine's oath and the Life Casket gambit.
With the Lich severely wounded and the Life Casket lost, and they had the assistance of the Elf Queen, a Legendary powerhouse… If they didn't deploy troops, they would truly be cursed for a lifetime, and it was very likely that they would be sent to a tribunal, where cowardice in battle would mean at least ten years' imprisonment.
But could that terrifying Lich have made such a big mistake? How could something like the Life Casket be stolen?
Wait, the Life Casket?
Allen remembered something, when they returned to their homeland from Alchemy City his father had a carriage full of stuff, and he seemed to have heard him mutter, "That Lich is outrageous, how could he have so many Life Caskets?!"
At the time, Allen, bearing his own guilt, didn't dare to ask more, thinking he had heard wrong.
Looking back now, could that carriage have been filled entirely with Life Caskets?