It is far more likely that everything, and not just IT, but everything collapses than we make it to the point you mention.
LLMs replace entry level people who invested in education. They would have the beginning knowledge, but there's no means to become better because opportunities are non-existent because they replaced these positions. Its a sequential pipeline failure of talent development. In the meantime you have the mid and senior level people who cannot pass their knowledge on, they age out, and die.
What happens when you hit a criticality point where production which is dependent on these systems, and it can no longer continue.
The knowledge implicit in production is lost, the economic incentives have been poisoned. The distribution systems are destroyed.
How do you bootstrap recovery for something that effectively took several centuries to build in the first place, but not in centuries but in weeks/months.
If this isn't sufficient enough to explain the core of the issue. Check out the Atari/Nintendo crash, which isn't nearly as large as this but goes into the dangers of destroying your distributor networks.
If you pay attention to the details, you'll see Atari's crash was fueled by debt financing, and in the process they destroyed their distributor networks with catastrophic losses. After that crash, Nintendo couldn't get shelf-space; no distributor would risk the loss without a guarantee. They couldn't advertise as video games. They had to trojan horse the perception of what they were selling, and guarantee it. There is a documentary on Amazon which covers this, playing with power. Check it out.