Your argument assumes premises that are hardly certain. We use automobiles to travel, yet tens of thousands can still ride horses today. Hell, there are thousands of blacksmiths and glass blowers. If there's a several hundred million dollar market for programming language experts, this will provide sufficient incentive for some people to remain sharp.
We still have COBOL programmers for a reason. The economic incentive to keep the skill never left.
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>linkregister: LLMs are trained with a large corpus of commercially available source code. However...
This concedes your point. Hence the following "however". It's bizarre to argue against it.