We've been playing with Pascal72 (who is angry after this ).
I viciously attacked a LBI in Pascal's Border with MC and its leader and did not destroyed it. Then Pascal was thinking about not rolling the dices for the battle back because of possible flag ; he had the cards (Double Time) allowing him to empeach the Cav retreating on his next turn.
So the question is :
Must a unit battle back if it's able to ? (In the rules, it's written "May ... if"
We think that a unit is not forced to do this but Pascal launched too quickly and got a flag and a red square (I laugh )
Thanks for your answers

If it's "may", it's not "must" !

Thank you for your quick answer Philippe : that's exactly what I said to my dear friend François (Hawkmoon).. but he is right when he says I clicked a little quickly on my button dices and could had rolled two "blues"...

I could seem strange to not automatically battleback, but I can confirm that in very particular cases (as described above), it can be more advantageous..

cheers,

Philippe answered it right.
I've just updated "Battle FAQs" for further reference.