Rule 104.5 · Ending the Game
If a player loses the game, that player leaves the game. If the game is a draw for a player, that player leaves the game. The multiplayer rules handle what happens when a player leaves the game; see rule 800.4.
Ask the judge Pro
The life counter has an AI judge that answers your play citing the exact rules. It is part of Gatewatch Pro; the rules, Oracle text and rulings stay free.