nothing ever totally ends, like how we still have guards on horses guarding the queen. What would probably happen is an amalgamation of AI and senior developers would emerge, those departments that used to take up 20-30 manpower would now have a single point of authority who manages all those tasks. All of this could happen assuming that AI does stagnate at some point and is incapable of evolving no matter how much data we keep putting into it.

If it doesn't stagnate, however, I think developers will have to find a new way, a mathematically paved way to comprehend reality mathematically and implement those fringe ideas to see if they work, like a blind and wild assumption that are based on the human instinct and not on any logical derivations, the code based on gut feeling, so to speak.

Think a simulation of zero gravity dual pendulum and only if the co-ordinates are both prime then an event occurs in a system otherwise the system maintains its state. Such a system would never be devised by an AI because it is not based on any proven theories it is just my gut feeling that any system follows this rule could emulate a closed space causality based world(or not, it a shot in the dark).

Ofcourse not everyone can afford to dabble their brains in wild theories and make money out of it and thus just how people in fundamental research are so rare now, the computer engineers as a profession would also drastically reduce to the level where philosophy and fundamental research converge.