Has the ER made the suggestion that he defer his $6500 (or more) to the 401k plan for 2017? I know participants have reasons for not using the 401k (i.e. investment flexibility), but he would get his tax deduction and his free money.
And if the buyer didn't agree to pick up the cost of the contribution, the seller could still do it after the termination of the plan and the sale of the assets. An asset sale means the seller as a corporation still exists. It might be winding down but part of that process is paying the remaining bills. In this case one of the remaining bills is the SH contribution.