In case die is overridden, you can call CORE::die instead.

Update: maybe I should mention that this wouldn't help much, though, if the die should somehow happen to be trapped by an eval { ... } block  (which I don't know)...  In this case, you could try something along the lines of

    open my $fh, "<", $file or warn "Couldn't open '$file': $!" and ex
+it;
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to force the program to terminate.

Consider this

my $file = "does-not-exist";

while (<STDIN>) {
    eval {
        open my $fh, "<", $file
            or warn "Couldn't open '$file': $!" and exit;
    };
    print STDERR "ERROR: $@" if $@;
}
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(which would actually terminate the program) vs.

while (<STDIN>) {
    eval {
        open my $fh, "<", $file
            or CORE::die "Couldn't open '$file': $!";
    };
    print STDERR "ERROR: $@" if $@;
}
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which would continue printing (despite the CORE::die)

ERROR: Couldn't open 'does-not-exist': No such file or directory at ./
+680735.pl line 10, <STDIN> line 1.

ERROR: Couldn't open 'does-not-exist': No such file or directory at ./
+680735.pl line 10, <STDIN> line 2.
...
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...if you keep hitting the ENTER key.

(If necessary, you could of course also use CORE::warn or CORE::exit in combination with the above...)