Thanks for your feedback Kazuki, but I'm unable to duplicate what you've described in testing.
HP and MP are restored to max if you choose to restart the battle; those actions are the very first two things in the Common event that runs when you make that choice. All events (e.g. slime army) are also set back to their original location.
Are you sure this is what you experienced? I've played through a few times and all is working as expected, but I may be missing something.