The corridors of the drones at maximum 400 feet and in principle not visible, only in case of anomaly, by the air traffic controllers. Helicopters at a minimum of 500 feet and the final descent to the heliports must be done vertically. The helicopters would also carry, even if they are controlled by humans, an automatic pilot that would take the controls in case something goes wrong.
I don't know, it's a quick example, I'm sure it has many drawbacks, but something could be done. But one important factor, the number of helicopters would drop very dramatically, even to extinction since the drones would be much cheaper in every way and could do the same functions easily.
We're imagining it, right?
P.S.: Anyway, I don't think we'll see it with our eyes. Although development is very fast, this kind of thing involving human personal security needs many years of development to be feasible.