Are they requesting a cash distribution or a rollover? If they are requesting cash, then it's fine.
If they are requesting a rollover, then there is the possibility that they could fail to take their RMD if they terminate before 12/31/2021. In order to avoid that possibility, they should take at least the amount that their 2021 RMD would be, if 2021 were a distribution calendar year, based on their account balance at 12/31/2020 and their current age, as a cash distribution and roll the rest over. It might help to remind the participant that if they fail to take their RMD there is a substantial excise tax that they would be responsible for.
If they ultimately refuse to take enough of their distribution in cash, and it later turns out that a 2021 RMD is required, then a corrected 1099-R should be issued showing the RMD amount as a taxable distribution and only the remainder as eligible for rollover. The participant would have to be notified that $X amount of their distribution was not eligible for rollover and should be removed from their IRA.