Would it be beyond the realms of possibility for that warning to be produced when a filehandle goes out of scope?

It's a default warning in 5.22.0 onwards:

$ perl5220 -e'{open my $fh, ">/dev/full"; print $fh "abc"}'
Warning: unable to close filehandle $fh properly: No space left on dev
+ice at -e line 1.
$
[download]

Dave.