I'm not sure. I don't say that "Tomorrow or Accident" I just know that we all will never know what tomorrow will bring. That is the Unknown. But I don't have a way to help you on this :(

I don't think there is an English phrase that means what you're saying. If this is a phrase that you want to translate into English, it might make sense (if I understand your meaning correctly) to say "Tomorrow or an accident -- you never know which will come first."