Sunlight

The sunlight is the main thing. Living systems are driven by sunlight so sunlight was the most important rule to live by. When the sun goes Nova then there will be an end and beings that have lived on the earth will have to go different ways. It might be like coming out of the dark and finding you are born in a different world but this one has the same main rule. Some rules of the new place will seem very distracting at first but then the ways of that world will take you over and you will never remember this place and you won't even remember the main rule was the same even though it is.

I don't know for sure about after the Nova,though.