If a player controls a Platinum Angel and their life total goes below zero, do they lose the game if Platinum Angel is then destroyed?

Platinum Angel reads: 'You can't lose the game and your opponents can't win the game.' While it's on the battlefield, it creates a continuous effect that overrides the normal loss condition for life totals dropping to 0 or below (CR 119.3).

State-based actions (SBAs) are what actually cause a player to lose for having 0 or less life (CR 704.5a). However, SBAs are also prevented by Platinum Angel's effect while it's in play. The moment Platinum Angel leaves the battlefield — for any reason, including being destroyed — that protective continuous effect ceases to exist (CR 611.2).

The very next time state-based actions are checked (which happens before any player gets priority after the Angel leaves), the game sees that your life total is 0 or less and you lose immediately (CR 704.3, 704.5a). Your life total does NOT reset; it stays wherever it was, and SBAs now apply to it normally.

Concrete example: Your life total is -5 and you control Platinum Angel. Your opponent destroys it with Murder. As soon as Murder resolves, SBAs are checked. The game sees your life total is -5 (≤ 0) and you lose the game on the spot — you don't get to take any more actions.

Note: If somehow your life total were raised back above 0 before the Angel was destroyed (e.g., you gained life in response), you would not lose once the Angel dies, because the SBA condition (life ≤ 0) would no longer be met.