He stays on track for Axis, pending fully figuring out his lich ascension, by checking with regular Early Judgment and routinely donating to Iomedae's Church.
Before meeting Keltham, Ri-Dul murdered a few extra people so he'd detect Lawful Evil to Keltham, whose notice insisted on that for whatever weird reason. Obviously, he's running the most absurdly expensive form of True Resurrection insurance for the length of his employment. After it ends Ri-Dul will donate enough to Iomedae's Church to get back on track for Axis, using a fraction of Keltham's payment.
Not that Keltham knows any of this, of course.
But yes, people who go to Hell are stupid. It's just that Golarion contains a very large number of very stupid people, including, apparently, some people who you would have thought otherwise too powerful and competent for that.