It is just like English sayings and phrases, there are Japanese sayings and phrases as well. It is called [kotowaza ことわざ].
What is the KOTOWAZA?
Kotowaza is the Japanese saying/phrases which expresses people’s wisdom and it has been told by many people from long time ago. And it is an example of something and a teachings of the life.
後は野となれ山となれ/ATOWA NO TO NARE YAMA TO NARE
Do not care what happens afterward. (even if it becomes a field or a mountain).
It might be similar to a French expression and an English expression.
After us (or me) the deluge/after us it may flood
How to use it
Ashita Kyu ni utanai ka to iwareta. Shikatanai, rennsyuu suru. Ato wa no to nare yama to nare. ,
I was suddenly asked to sing songs tomorrow. No much I can do but do practicing. I do not care what happens afterwards.