Idk how you're bad enough to let them die tbh Never had anyone die on me I think I heard you have to restock troops at the barracks
Just follow my guide i made and if your hero "dies" just chill on exploration and level him up and make sure to go to the visitation station in the tavern
While you are exploring, you'll encounter these certain spots where you can heal a single character's units. Not sure about the exact name of it, but you know what I mean
1 is a little slower but has like no fights aside from the boss man idk i think i got lucky with my units because i got some chick who has 500 leader ship after i gave her a hat that boosts her lead