If the participant died after his required beginning date but did not receive the RMD for the year in which he died, you will use the participants info to calculate that year. All subsequent years will be based on comparing the participant’s Single Life Table factor (-1) to the oldest beneficiary’s Single Life Table factor and choosing the greater life expectancy factor for the calculation. Essentially, here, choosing the oldest son’s factor each year. The SECURE Act changed the rules for participants who died after December 31, 2019 by eliminating the lifetime payment option and the five-year method. My guess is that if it was started using the life expectancy method, it can continue that way, but I would suggest seeking more formal advice on this particular situation.