Well, is not easy, but if you have time what you do is you keep track of all the top teams in all the leagues in your case it was D4, that way you get an idea if you will promote even if you don't win your league.
How you do it is you go to your current league standings, and click on the USA flag next to your league #, that will take you where you can select all the leagues in whatever division lvl you want to see.