So the following seems to do exactly what I want, but doesn't handle empty fields. It might not matter, because my input shouldn't have any empty fields. I'll probably just check that my input string doesn't begin or end with a delimiter, or have two consecutive delimiters in the middle anywhere. If it does, it's bad input, and I can just throw it out. Would still be fun to know how to handle empty fields, though...

my $re = qr{
  (?>      # don't backtrack into this group
     !!    # either the escape character,
           # followed by an escape character
     |     # or
     !;    # escape followed by delimiter char
     |     # or
   [^;\n]  # a character that is neither delimiter
           # character or a newline
  )+
}x;


while(<>) {
    chomp;
    my @aray;
    $str = $_;
    print "$_\n  ";
    while ($str =~ /($re)/g) {
        $s = $1;
        $s =~ s/!!(?=(!|;|\z))/!/g;
        push( @aray, $s );
    }
    print join(' | ', @aray) . "\n";
}
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