Edit in JSFiddle

var win = window.open("http://www.google.it",'','height=500,width=500');
var winTimer = window.setInterval(function()
{
    if (win.closed !== false)
    {
        // !== is required for compatibility with Opera
        window.clearInterval(winTimer);
        alert('POP-UP CLOSED...');
    }
}, 200);

SCRIPT CHE RECUPERA L'EVENTO CHIUSURA DI UN POPUP