IT and CS, combined, is the only field I know of that both pays really well and requires no formal education. I know a great many self-taught people, and a great many more whose EE/CE/math/physics/economics jobs required learning, so they did, and never looked back.
Having said that, the barrier of entry is higher without a BS. Someone with a lot of experience, and proof, can often skip the degree entirely. But as more and more resumes are scanned by computer (or illiterate monkeys who should never be making interview decisions), the lack of degree will automatically disqualify them from many jobs without second thought. This means a lot of job advancement comes through networking.
Realistically, entry level can be done with the associate's without huge issue. Further advancement can be accomplished by internal promotions, by knowing where to submit your resume to skip the beancounters and the machines, and go right to the hiring managers, or through taking a step back and finishing the full degree.
Also the good news is that quite a few companies will pay for employees to get their degrees.
So. In short. Will it prevent him from getting a job? No. Will it make it harder? Probably. Will it prevent career advancement? No. Will it make it harder? Probably.
Of course, another thing to consider - if getting the BS requires two full years of work, that's a sacrifice of about $40k/yr (plus 15k, minus 10k, depending on location) in addition to all the school expenses. Therefore it has to be done very carefully and deliberately; otherwise one might find themselves earning 5k/year more with a BS than an AS, which would take a decade and a half to make up for the lost wages, and even more to make up for the tuition.
