[Mean]

@ the top:

pawn Код:

forward dead( );
new deada[ MAX_PLAYERS ];

Will make a callback for the repeating timer and will check if player is dead

pawn Код:

public OnGameModeInit( )
{
    SetTimer( "dead", 5000, 1 );
    return 1;
}

Will start the timer to check if everyone is dead

pawn Код:

public OnPlayerDeath( playerid )
{
    deada[ playerid ] = 1; 
    return 1;
}

pawn Код:

public OnPlayerSpawn( playerid )
{
    deada[ playerid ] = 0; 
    return 1;
}

Will make the server know if player is dead or not.

pawn Код:

public dead( )
{
    new count = 0; 
    for( new i = 0; i < MAX_PLAYERS; i++ ) 
    {
        if( deada[ i ] == 0 )
        {
            count++;
        }
    }
    if( count == 0 ) 
    {
        for( new a = 0; a < MAX_PLAYERS; a++ )
        {
            if( IsPlayerConnected( a ) )
            {
                ForceClassSelection( a );
                SetPlayerHealth( a, 0.0 );
            }
        }
    }
    return 1;
}

If everyone is dead at the whole server, it will put them at class selection!
UNTESTED.