Maybe instead of this changing the mechanics too much, hospitals could simply reduce the overall casualty rates calculated in a particular attack without altering the win/loss calculation? So say I have 10k soldiers, 2 hospitals, and I lose the war. Again, for purposes of discussion, lets say my current casualties would be 2k. Yikes. Now since I have 2 hospitals, even though I've lost that war, maybe I get to save, I don't know, maybe an extra 10% of casualties per hospital, so 400 soldiers saved? I've still lost the war, but instead of ultimately having 2000 casualties, I only have 1600. That would greatly reduce the impact on gameplay while also allowing hospitals to be useful.