You must resort to the old coin toss again.
Heads, and your cavalry roll up the wings, then defeat Harold's center: you win the battle.
Tails, and your cavalry is either defeated or is simply too mauled to face Harold's center: he beat your infantry and is waiting now in a compact shieldring, daring the dregs of your cavalry force to come close. The battle is a stand-off, which means that you have lost. Harold's army will continue to get stronger; yours has taken a severe beating. Back at Hastings, you find that your numbers have been reduced to roughly half. There is really nothing left for you to do but throw in the towel and sail back to Normandy. William the Bastard is what you remain forever.