// Somewhere on the top of the script   
#define Max_Event_Players 69
enum E_Players {
    EventPlayerId,
    bool:isAlive
}   new EventPlayers[ Max_Event_Player ][ E_Players ];
new EventPlayersCount = 0;
new bool:IsPlayerOnEvent[ MAX_PLAYERS ];

public OnPlayerConnect( playerid ) {
    IsPlayerOnEvent[ playerid ] = false;
}

public OnGameModeInit() {

    for( new PlayerId = 0; PlayerId < Max_Event_Players; PlayerId ++ )
    {
        EventPlayers[ PlayerId ][ EventPlayerId ] = INVALID_PLAYER_ID; // meaning e.g. this player is not active, died, this slot's free, or something
        EventPlayers[ PlayerId ][ isAlive ] = false;
    }
    
}

public OnPlayerDeath( playerid, reason ) {
    if( IsPlayerOnEvent[ playerid ] ) {
        // When player dies, we assume, that he quits event automatically.
        IsPlayerOnEvent[ playerid ] = false;
        EventPlayersCount--;
        EventPlayers[ SlotId ][ isAlive ] = false;
        EventPlayers[ SlotId ][ EventPlayerId ] = INVALID_PLAYER_ID;
        
        if(EventPlayersCount == 1)
            FinishEvent();
    }
}

// In the deeps of the bits
stock AddPlayerToEvent( playerid ) {
    new SlotId = 0;
    while( EventPlayers[ SlotId ][ EventPlayerId ] != INVALID_PLAYER_ID ) // Find next free slot
        SlotId++;
    if( SlotId == Max_Event_Players )
        return false; // cannot add anymore players
    EventPlayers[ SlotId ][ EventPlayerId ] = playerid;
}
// Somewhere else
stock StartEvent( ) {
    new SlotId = 0;
    while( EventPlayers[ SlotId ][ EventPlayerId ] != INVALID_PLAYER_ID || SlotId < Max_Event_Players) {
        EventPlayers[ SlotId ][ isAlive ] = true;
        EventPlayersCount++;
        SlotId++;
    }
}

// Yet in another place! Wow! :V
stock FinishEvent() {
    // Find the winner in EventPlayers... Because only he's there, if we follow our convention mentioned in OnPlayerDeath callback
    new SlotId = 0;
    while( EventPlayers[ SlotId ][ EventPlayerId ] == INVALID_PLAYER_ID )
        SlotId++;
    
    // Here you can do whatever You want, because SlotId now contains ID of the player which is the only one left in the event.
}