Slitherine

While playing the dark elves I was enjoying invading, wounding/burning and retreating. I got into the situation where I had a second hero helping protect my capital and my ranger hero had to retreat back into the same province because there was no where else to retreat to. This resulted in me losing my ranger hero Losing a hero when I didn't lose any troops is annoying, but not being able to choose which hero I lost just added salt onto the wound.

You do have to be aware that units and heroes which cannot retreat will be lost (or they may be captured, depends on the exact situation).

Always a good idea to be sure of a possible retreat path if you expect a fight.