Ah, upon closer inspection, the reason the END block isn't called is from the KILL line.

 # $SIG{HUP} = $SIG{INT} = $SIG{QUIT} = $SIG{TERM} = sub {
 #    $SIG{INT} = $SIG{$_[0]} = sub { };
 #
 #    CORE::kill($_[0], $_is_MSWin32 ? -$$ : -getpgrp);
 #    for my $_i (1..15) { sleep 0.060 }
 #
 #    CORE::kill('KILL', $$);
 #    CORE::exit(255);
 # };
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There is no guarantee to which END block is called first by Perl. MCE::Shared has an END block to notify the shared-manager to exit. The script will stall had Perl called that one first. Therefore, leave intact the sig handling bits at the application level. The END block is not necessary. But simply added to see workers enter it.

use strict; use warnings; use feature 'say';
use Data::Dumper; ++$Data::Dumper::Sortkeys;
use Time::HiRes 'sleep';
use MCE::Loop;
use MCE::Shared;
$|++;

my $pid = $$; say "PID $pid";
my $hash = MCE::Shared->hash();

$SIG{'INT'} = $SIG{'TERM'} = sub {
    my $signal = shift; $SIG{'INT'} = $SIG{'TERM'} = sub {};
    say "Hello from $signal: $$";
    say 'Parent is ready to dump';
    say 'Dumping: ' . Dumper $hash->export;
    MCE::Signal::stop_and_exit('INT');
};

MCE::Loop->init(
    max_workers => 2, chunk_size => 1, user_begin => sub {
        $SIG{'INT'} = sub {
            my $signal = shift;
            say "Hello from $signal: $$";
            MCE->exit(0);
        };
        $SIG{'TERM'} = sub {
            my $signal = shift;
            say "Hello from $signal: $$";
            MCE::Signal::stop_and_exit($signal);
        };
    }
);

mce_loop {
    my ( $mce, $chunk_ref, $chunk_id ) = @_;
    say sprintf 'Forked worker in slot %s with pid %s for chunk %s', M
+CE->wid, MCE->pid, $chunk_id;
    for ( @{ $chunk_ref } ) {
        $hash->{ sprintf '%.2d %s', $_, $$ } = time;
        say "After $_: " . Dumper $hash->export;
        sleep 3;
    }
} ( 0 .. 12 );

MCE::Loop->finish;

END {
    say "Hello from END block: $$";
    if ($$ == $pid) {
        say "Parent is ready to dump";
        say 'Dumping: ' . Dumper $hash->export;
    }
}
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I will make a new MCE::Shared update after more testing. Thank you, 1nickt.