One could argue slippery slope in regard to suppression of such information leading to similar attitudes on the part of government in other areas, but sometimes it's better to slip partway down the slope than stay at the top of the hill.
When there is nothing you can do about a situation, when it truly is outside of everyone's control, the determining factor in regard to making information public should be, "How will people react?"; will releasing the information result in a worse situation for the majority than if the information is suppressed, is a valid concern.
The liberal librarian in me says release the information that can be verified as true, the pragmatist in me says that if the world is going to end in five days, nothing we can do in that time period will make a difference so let people go about their lives as normal, and the second is the perspective that should be taken in this matter. "First, do no harm," to paraphrase the Hippocratic Oath. If you can't make the situation better, don't take action that will make it worse.
Now, if I was a believer in a religion that said that one needed to be sanctified to go to Heaven after death, then my perspective would change in an end of the world situation, as I'd want to provide the opportunity for as many as could come to faith in that period as possible to do so, so I'd want them to have that sense of immediacy in making such a choice.