Distribution from Terminated Plan

We have a plan that was terminated 12/31/2017. IRS considers a plan terminated if all assets are distributed within 12 months of the termination date. 

There are two participants who could not be located and the client directed 100% of each participant account payable to an eligible rollover institution that accepts and establishes IRA rollovers for missing participants.

The checks were prepared last week and mailed to client, payable to the financial instution.  If the checks are mailed ASAP to the rollover institution, is the plan closed since the money came out of the plan; or is the plan considered when the rollover institution establishes the IRA accounts?

2 hours ago, thepensionmaven said:

There are two participants who could not be located and the client directed 100% of each participant account payable to an eligible rollover institution that accepts and establishes IRA rollovers for missing participants.

Is this what the Plan says?

Yes, but that's not the question.  Is a plan terminated when the money is out of the plan account or when an IRA is actually established.

Difference will mean another set of 5500s

If the check(s) is(are) written, I consider that to be a completed distribution.  If someone voluntarily set up an IRA, and the check was cut on Dec 1 but not deposited until January, there's no way I would consider that not paid out in December.  Same situation really.