If you believe in the signaling theory, however, his marginal product is fairly low, much lower than the wage he will be paid. They will fire him. He'll come out a bit ahead, if he is not too demoralized, but within a few years he will be paid his marginal product.
The central problem with the signaling theory is that a worker's productivity is observable. Why pay a large wage premium to somebody indefinitely regardless of their actual productivity?
My views about how education raises wages:
1. Certainly for some people, education adds to skills. However, I believe that for many other people, it does not. My main complaint with those who favor expanding college education is that they do not measure carefully enough along the right margin.
2. Education adds some of it value due to credentialism. The hypothetical fake college degree will get you a better salary in government pretty much automatically. And, no, you won't get fired when it turns out that your productivity fails to match your credentials.