What will happen when Son Heung-min retires.

First of all, Japan will demand regular matches.
The opposing teams will have an easier time due to the loss of a striker who accounts for 1.5 players' worth of impact.
The number of "grand" matches against teams ranked 40th–60th in the FIFA rankings will increase.
We might even start losing games.
There will be a high possibility of struggling heavily against China, Uzbekistan, or Qatar.
Instead of worrying about finishing 1st or 2nd in the group stage, we'll be worrying about 2nd or 3rd.
Frustrating football becoming the norm is a given.
Oh Hyeon-gyu, Bae Jun-ho, Cho Gue-sung, Lee Seung-woo
We might be able to watch world-class attacking power.
We might see a repeat of the 2004–2010 era.
Frustrating Asian Cup matches will take place.
We will be able to compete on equal footing with teams ranked 60th–100th in the world.
Difficulty in breaking through will be standard, and they'll just perform "sideways ball circulation" maneuvers;
"Do it for us" football will be impossible.
We could seriously and extremely regress to "long ball" football.
The void left by Son Heung-min and Lee Jae-sung
Cannot be filled by Kim Min-jae, Lee Kang-in, or Hwang In-beom.
Hwang Hee-chan's aging process has already begun.
For now, referees and European national teams
Might start looking down on the Korean national team.
It is obvious that the global perception of Korean football will decline.
Hiring foreign managers and the decline of Korea's name value will be inevitable.
World ranking 35th–50th range
A regression to the 2014–2015 era,
when Son Heung-min was in his mid-20s, is possible.
If we don't produce a genius-level attacker who plays in the top 5 leagues
by the age of 20 (high school senior to college freshman),
we will likely struggle for the next 5–8 years.
Korean football will find it difficult to match up against world-class teams.
The '96 liners will be eaten alive even more miserably by their juniors...
This is a scenario from 3–4 years ago.
The '91–'92 liners are the last generation, and
conflict with the generations below them will begin... haha