The question is how can I force the specific clean up in case of an abnormal exit (i.e. croak) of each helper script?

As always, TIMTOWTDI. Here's one approach (helper script):

use warnings;
use strict;
use Carp;

my $cleanup = sub {
    print "helper cleans up after itself!\n";
};
local $SIG{__DIE__} = $cleanup;

print "Hello\n";
croak "bad thing";
print "There\n";

1;
[download]

Running that with your main script of the OP gives:

qwurx [shmem] ~ > perl main.pl helper.pl 
Hello
helper cleans up after itself!
helper.pl: bad thing at helper.pl line 11
        require helper.pl called at main.pl line 6

Done with main
[download]

See %SIG. The local __DIE__ handler is made into an anonymous subroutine assigned to a lexical variable in order to not pollute any namespace.

update:

Reading the documentation I linked to, I find the following:

Due to an implementation glitch, the $SIG{__DIE__} hook is called even inside an eval(). Do not use this to rewrite a pending exception in $@ , or as a bizarre substitute for overriding CORE::GLOBAL::die() . This strange action at a distance may be fixed in a future release so that $SIG{__DIE__} is only called if your program is about to exit, as was the original intent. Any other use is deprecated.

So... that might be not that sound an advice as I thought it would be. I disagree with this being an implementation glitch, though. A do file should die in the same way as a use, which is also eval at its core. But it is not clear whether the glitchiness applies to all sorts of eval.