Koln probably does not have much chance of avoiding the relegation this season. And as you said, the Bundesliga 2 is also full of strong teams. So it is going to be hard for whichever team that gets relegated to actually get the promotion again.
Mainz does still have a chance though. The problem is they are going to play against Dortmund and Wolfsburg in the next two matches that are left for them in this season. And on the other hand, the team that they are actually trying to get ahead of, union Berlin, is going to play against Koln and Freiburg in the next two matches. So it does look like Mainz is going to find it hard to avoid relegation even though they are only one point behind Union Berlin
That is likely to happen in Koln and Darmstadt they can not recover anymore while Mainz still has a chance to take the spot again in the Bundesliga 1st division, and not only this season we will have a new champion and because Bayern Munich right now can not do a thing about it as the points difference was enormous for the Leverkusen it was 84 to Bayern Munich's 69 it was really a shame for the defending champion but this season we got a new champion in the Bundesliga.
Its very hard to get back from the second german league into the first german league , there are so many teams that trying this now for years.
The most problem is that the most or many players will leave the team when you goin down into the 2 league.
For sure it is really hard for a team in the 2nd division to get into the 1st division as many teams would want to get into the 1st division and if a team would likely get regulated then that team will need to get back into the hardship once again, but I really feel sorry for the Bayern Munich but for me it is good that we have a new Champion team but learning the truth that Bayern Munich is pretty much not the defending champion next season.