I don't know that the situations you or I so simply hypothesize can or have or will actually exist in real life, but I will take a stab at answering your question.
IF I am sure that there is no seeded backup
AND I think that the perp might shoot someone
AND my state permits me to shoot in those circumstances
OR (I think the perp might shoot me
AND there is no seeded backup)
OR I think the perp will shoot me
THEN I will shoot him in the head repeatedly without warning
OTHERWISE I will not even think about my gun.
As far as your relatives or self being in the position of the teller, I advise you and your relatives to move to Texas and don't bother trying to lay any guilt trips on me for YOUR personal choices. I don't blame anyone in Texas for my living in MA, and I don't expect them to blame me for where they live. You want to be protected, hire a bodyguard or buy your own gun.