I would split on everything that is not a bare comma (untested):

my $q_str = qr("[^"]*"); # quoted string
my $unq_nc_str = qr([^",]+); # string with no quotes or commas
my $esc_com = qr(\\\\,);  # escaped comma
my @bits = grep {$_ ne ','}
                split /((?:$q_str|$unq_nc_str|$esc_com)+)/, $line;
[download]

By grouping the split regex, we get split bits as well as bare commas. Then we filter bare commas. This assumes that quotes are not nested.