Ignore the sale for a moment, and ask the same questions.
Can the plan terminate as of March 1?
how is safe harbor impacted?
If yes, what is the last pay date that is included as plan compensation?
Typically this would be the last pay date on or before March 1 if that is the termination date.
Once you figure out the answers to the questions above, then move on to the next question,.
Does the pending/ anticipated sale change any of the answers?
Removing the participating employer on the transaction date is fairly easily done.
I can’t imagine “removing” the participants as of the transaction date. It’s either a distribution or a spinoff and that will all likely take way more time.