With one day's warning, the evacuation discussions are moot. Better to discuss proactive measures. There are professionals in the astronomy community who take this possibility seriously--it isn't a question of if but when. They see it as inevitable at some point and since we don't have any other place to live we need to protect Earth if we can.
Hopefully we have time to develop a defense--we are a moving target so there's that in our favor. There are several ideas out there--some are majorly wrong-headed. For instance, firing a nuke at an incoming asteroid or comet, which would result in a hundred fragments headed our way instead of one body--kind of like grapeshot.
The best idea I've heard proposed is to use a space-based mirror to reflect focused solar energy onto an object to create a reaction which would change the trajectory of the object. No complicated missions to rendezvous a space tug with the object to push or pull it off course, etc.
The mirror idea still requires financial commitment and preparation time and good sky surveys--especially in the southern hemisphere where surveys are sorely lacking. And there is always the chance that we'll only have one day's warning (or none at all). But we ought to at least try while we (maybe) have time. Someone (I forget who) said that the difference between us and the dinosaurs is--we have a space program.