Thank you for playing! There are definitely fixes that I would love to do once I'm able to update the game.
The hero spawns with health and attack based on your slime's level when you leave the cave, so for slimes determined to kill a hero a good strategy is to leave the cave while a hero is present and very quickly level up once or twice before finding the hero, which will put you at an advantage. It is very unlikely for a regular slime to defeat a hero, although it is technically possible :)