every day life

Someone is always putting a date on the end of the world. Apparently the next one is March 21st. I tend not to worry about these things too much, after all if cataclysm is coming there is not much I can do about it. But the question is, if I knew for sure that the world was ending on a certain date and that there was no escape then what would I do.
It is an interesting question, because although I am not particularly worried about predictions and foretellings there is something to be said for asking the general question as a way thinking - if I felt some urgency to be right with God because of some impending doom what would I do differently.
There seem to be two questions at play. The more general one was faced by the early church who, soon after the death and resurrection of Jesus, believed that the end of time was going to be soon. The early epistles are full of urgency, telling believers not even to worry about getting married if they could live a single life, so that they could focus on preaching the Gospel. As time went on, it became obvious that time was not about to end, and more developed and lasting theologies and practices came about.
We live in a time in which, despite the doom and gloom merchants, we are not thinking the world will end tomorrow. Whilst we are called to develop a sense of detachment from our things and to live in a way which honours all creation as belonging to God, we have to balance this with day to day living in a way which is responsible - so that we can feed and clothe our families and ourselves and help those around us. This particular balancing act is a unique call to each of us.
However, there is another part of thinking about what we would do differently which does speak to every day and sustainable life. When we ask ourselves questions about how we would feel we would need to change to live a very deliberate last day, to value God and those around us, to smell smells and see beauty. These sorts of questions about taking notice and living carefully can apply to every day, they do not need to be left until some last minute emergency plan.
John Keble says it well in the hymn "New Every Morning is the Love" in this verse:
The trivial round, the common task,
Will furnish all we ought to ask;
Room to deny ourselves, a road
To bring us daily nearer God.
Our road to God is often through very carefully and deliberately living every day and thinking about how we might live a mythical last day might be a good spiritual exercise to reveal those things which we already know we might be doing better.