If your life total is brought to 0 or less at the same time that creatures you control are dealt lethal damage, you lose the game before the last ability goes on the stack.

If one or more creatures you control die at the same time that Bastion of Remembrance leaves the battlefield, its last ability triggers for each of those creatures.

In a Two-Headed Giant game, Bastion of Remembrance's last ability causes the opposing team to lose 2 life and you to gain 1 life.