There seems to be an example in the Yom Kippur War that Israel won a victory in decades ago. Any religious obligation may and ought to be abrogated for the sake of defending a life.
That said, if it’s made known that there are guards (even if not obvious who they are) the cowards will back off almost to the last one and there will never be a shootout.
Going last night was very edifying to my Christian faith and Conservative principles. Someone at the service even quoted the Founding Fathers about the "Right to life, liberty..." They expounded that liberty meant the inalienable right to practice your faith without the fear of hate and violence. Everyone there I think at least for one night agreed how blessed we are that we live in such a great country that people still value that. And as a former practicing Jew, it also made my heart full that unlike 1938 in Germany, people stood up and said killing Jews because they were Jewish was not right and we stand here and grief with you. History had not been all that kind to my tribe.
As far as the motivations of the Muslims at the service, I am not one to judge their sincerity. The Muslims I know just want to live their life unmolested and practice their faith and be judged on what they do, not what the terrible things their wackadoos perpetrate.