How to never lose a hero or have to retreat

Before you embark on a mission, go to: Program files (x86) > Steam > userdata > 879448002 > 262060 > remote. There you should find your saves labed as profile_X (as seen below)
Copy all these 'profile' files and paste them in a folder to use as a backup, Mine was on my Desktop.

Do this before you go on any mission.

Let's say you got bad RNG or just made a mistake and you wish to go back in time before you went to that dungeon. To do this, Go to the folder where you backed up your save, Copy those files and head back to where you found them in the first place and paste them there. When you open the game again and open your savefile you'll be back in the hamlet before you embarked.

Here are a few achievements that are made easier or less detrimental by this method:
You can also do this in the middle of dungeons and during a battle, In case you wanna go for a Shambler trinket or something.