Without the answers from SO, ChatGPT quality will decline as well.
Wait 2-4 years for new tech come up, ChatGPT won't have the training data and noone is answering on SO anymore. You would just get wrong answers.
Tracing the fix-it sessions backwards in time to the broke-it sessions (such that the AI can learn from its mistakes) might be tricky unless we somehow manage to connect copiloting sessions through git history. Imagine a big database of changes where the AI is waiting to see whether the code persists, or if somebody comes along and fixes it.
so is github...
One can hope, anyways.