Under section 1.401(a)(9)-6 Q&A-12(b), the actuarial value of the rider must be taken into account when valuing the annuity for the purpose of calculating RMDs (except that in certain cases the actuarial value of the rider can be ignored if when added to the account balance the total is less than 120% of the account balance). Only the annuity company can do this valuation, and they are required to provide you with this value near the beginning of the year following the year-end valuation date. They must also provide this FMV on the Form 5498 that they file with the IRS. It's this valuation that you use to calculate the RMD for the year.
https://www.law.cornell.edu/cfr/text/26/1.401(a)(9)-6
Given that the rider provides a lifetime benefit, even though the account balance may go to zero, the valuation will never be zero after taking into account the actuarial value of the rider.
