Spot on Jim. The actual wording from the Rulebook (Pg. 13): "Even if models are already in base-to-base, a model wishing to fight must declare a Charge action to do so."
Here's how your options break down after a first action combat:
Draw, or both models remain Normal
- No choice here; must stick around and spend the second action on a Charge to fight again.
Opponent is Face Up or Face Down
- You may choose to walk away without penalty, or to declare a Charge and fight again. If the opponent is Face Down, they are automatically removed as a Major Injury.
Remember that after winning the 'hit' roll, you also always have the option to move 2" away rather than rolling to Wound.