GPT is good because of collective knowledge, lots of data. What do you have in mind by "hire experts"? Isn't that what we have now? Many experts in many fields, hired to do their work. Cut this number down and you reduce training data.
Let's assume that GPT eliminates an entire field of experts, runs out of training data, and whoever is at the helm of that GPT program decides that it's lucrative enough to obtain more/better data. One alternative is subsidizing these experts to do this type of work and plug it directly into the model. I don't expect the nature of the work to change, more likely it's the signature on the check and the availability of the datasets.
It's important to note however, that GPT does not itself have any knowledge, only information. Knowledge implies it has comprehension or understanding. It can just as easily produce bad information as good and it has little to no ability to self-assess the accuracy of information it provides.
You also may underestimate how quickly that AI could pass expert level. The experts out there still have many years of life left so they won't be disappearing soon. If we get self improving/self training AI sooner than later then, we'll humans won't be the experts.
