I'd imagine that no matter what it takes, you can't actually accept a certification that was made under death threat, especially when it was quickly rescinded. My guess is that once Trump heard of the threats, he sent over some agents to protect them and their families, which is why the reversal was made. The threat was timed to force them to make the certification, and the people needed to get their families safe before they could reveal that the certification was false and made under threat of death.

So no matter what, with credible proof of death threats, they can't really say, "Oh but you certified it". To allow such a thing would only make it convenient for people to send death threats at specific times to specific people, during every election. It is easy to see that the certification made under threat of death was never valid to begin with.