DB/DC Combo - Timing of Termination Amendment Adoption

[Towanda]

We have a client who is historically non-responsive and difficult to work with, so we were very excited when they decided they wanted to terminate their 401(k) and Cash Balance Plans. 

To ensure everything took place that needed to take place, we mailed notices out to the participants and gave the client 45 days to return the signed termination amendments.

The client has 2 more days to get the executed termination amendments back to us.

I've never had a situation where a client never signed and returned a termination amendment, and I can't find anything that points to this in particular.  Suppose the termination date comes and goes and we still have not received the signed termination amendments.  Is it okay that the client signs the amendments after the plans' termination dates?  (The Cash Balance Plan is not subject to PBGC by the way).