There’s 2 scenarios here:
1. The Admiral holds back and lets himself get killed, meaning there’s no more Admiral there to prevent Xebec from doing whatever he wants in the Holy Land
2. The Admiral goes all out, saving his own life, at the cost of doing some damage to the Holy Land.
Either way, the safety of the Holy Land is entirely at Xebec’s discretion, he can destroy the entire place if he so desires after killing you, so why not just say fuck it and go all out?