I think this would be a good add as an option. Yes. Maybe they could implement this as part of a Difficulty set.
So, if I choose Story Mode Difficulty or Exploration Mode Difficulty, or something like that, I have the ability to Undo my last combat action. This would be for players who are just learning the game and need to be able to experiment, as you say.
I really think Larian would put to rest a lot of issues with gameplay if they focused on Difficulty settings. Give players who want die hard D&D 5e ruleset their ability to play using absolute strict D&D 5e ruleset. Give players who want to focus more on story and less on rules the ability to do so. Give players who want a more relaxed, casual, exploration gameplay the ability to do so, etc.
This game requires a much more robust Tutorial. I think there should even be a Tutorial Mode that you can play that provides you with strategy tips even as you continue beyond the Dank Crypt, etc. As you are playing, the game points out certain things you could do to make each scenario easier. Example: You are about to face the Red Caps during the hag scene. Tutorial Mode provides a tip saying, "Don't use your spells as much on this fight unless you have to. This is not the boss fight. You will face the hag later." Another Example: Tutorial states, "This enemy has high defense. If you maneuver behind this individual, it is easier to hit them. Try to get your characters behind the enemy if at all possible."
This would go a LONG way.
