Several teams such as Liverpool, Barcelona, Arsenal and several others have been considered to automatically qualify for the round of 16, while other teams in the playoff zone have to work hard to win the same ticket.
We know which team can be the favorite at this stage and which team has the best chance of winning the ticket, but nothing is certain because each of these teams will do the best job possible in hopes of getting to the round of 16. The top team can lose, while the bottom team can win, this is not impossible.
I also do not think anything will change much for those that already qualified for the round of 16, there's still a chance for those on class one playoffs( Likes of Dortmund& Bayern) to still overtake LOSC or Brest
If the game goes in favour for them and vice versa for the other teams .
Thus, for the second class aswell... it holds same just as you've said the top team can loose while the bottom wins , which means both sides will have to fight for their survival although one is on a more safer side than the other but any mistake they drop and that's if the bottom wins their next game