The card Exquisite Archangel from Aether Revolt has the following ability:
If you would lose the game, instead exile Equisite Archangel and your life total becomes equal to your starting life total.
The way this works with losing due to life loss seems relatively simple, but what happens if you lose to something else, such as poison counters, mill, or an effect that says that your opponent wins the game? Does this ability have any other common edge cases?