valuation date or calendar year for calculation?

A 401K, plan terminating in 2017, last day of plan year 2017 would be the dat all assets distributed, which I do not know yet, but obviously would be the month all assets out of the plan.

Either I am not understanding the question or I think it is moot. 

You seem to be saying that the plan is terminating in 2017 and the last day of the plan year was a day in 2017 when all the assets were paid from the plan. 

So are you saying as of some day in 2017 everyone's balance was zero because all of the assets were paid out of the plan in 2017 correct? 

To me then there are no RMDs due for 2018 from the plan as everyone's balance in the plan is zero.  If they rolled their 2017 payment to an IRA in 2017 then there would be an RMD payment from the IRA using the 12/31/2017 balance in 2018. 

The payments made in 2017 from the plan ought to have had any needed RMDs for 2017 done as you were paying the plan assets from the plan based on the 12/31/2016 balance.

Am I not understanding the question or does that seem to answer your question? 

I think ESOP Guy's answer is spot-on, but I'm trying to figure out how the accountant might be looking at it.

The only place I can think this would even be questioned is a non-calendar year plan that is not valued daily, and maybe the accountant is concerned with a scenario where the plan year ends (say) 9/30/17 but final distributions don't happen until 12/15/17.

The 2018 RMD would be based on the adjusted 12/31/2017 account balance. That would be the balance as of the last valuation date (9/30/17 in this example), adjusted for contributions, forfeiture allocations, and distributions prior to the end of the calendar year -- so assuming everyone is fully paid out by 12/31/17, that should make everyone's adjusted balance $0, hence no 2018 RMD.

Alternately, if everyone has been paid out on the last day of the (short) plan year, then the account balance as of that date is $0 and there are no adjustments (since you're neither allocating to nor paying out from a terminating plan), so the 12/31/17 adjusted balance is still $0, so no 2018 RMD.

1 hour ago, ESOP Guy said:

To me then there are no RMDs due for 2018 from the plan as everyone's balance in the plan is zero.  If they rolled their 2017 payment to an IRA in 2017 then there would be an RMD payment from the IRA using the 12/31/2017 balance in 2018. 

The payments made in 2017 from the plan ought to have had any needed RMDs for 2017 done as you were paying the plan assets from the plan based on the 12/31/2016 balance.

I agree, and think it's just being overthought.