On linux, I'm thinking you could make your status_bar a toplevel widget, and you could do something like this snippet

#!/usr/bin/perl
use Tk;
$mw = MainWindow->new;
$mw->title("MainWindow");
$mw->Button(-text => "Toplevel", -command => \&do_Toplevel)->pack(  );

MainLoop;
sub do_Toplevel {
  if (! Exists($tl)) {
    $tl = $mw->Toplevel(  );
    $tl->title("Toplevel");
    $tl->Button(-text => "Close",
                -command => sub { $tl->withdraw })->pack;
  } else {
    $tl->deiconify(  );
    $tl->raise(  );
  }
}
[download]

Here is an example which signals the MainWindow if a toplevel window is closed. I'm sure you can find a way to work it in to your script.

#!/usr/bin/perl -w
# waitwindow.pl 
use Tk;
use strict;

my $mw = MainWindow->new();
my $toplevel_count = 0;
my $last_window_died = 1;

$mw->Checkbutton(
    -text => 'No toplevel windows alive',
    -variable => \$last_window_died,
)->pack();

$mw->Button(
    -text => 'Create a toplevel',
    -command => sub {
        my $toplevel = $mw->Toplevel;
        $toplevel_count++;
        $last_window_died = 0;
        $toplevel->Button(
            -text => 'Destroy Me',
            -command => sub {$toplevel->destroy}
        )->pack();
        $toplevel->waitWindow;
        #main window keeps processing events... 
        #this code is executed after $toplevel is destroyed 
        $toplevel_count--;
        if ($toplevel_count == 0) {
            #toggle the checkbutton 
            $last_window_died = 1;
        }

    },#end sub 
)->pack(
    -fill => 'x',
    -expand => 1,
);

$mw->Button(
    -text => 'Quit',
    -command => sub {$mw->destroy},
)->pack(
    -fill => 'x',
    -expand => 1,
);
MainLoop();
[download]