If the financial sector is somehow shut down, or radically shrunk, they'll just go to the next most profitable industry. Doctors get paid a lot, but there are sharp constraints on supply, so you'd just have more competitive medical schools, as opposed to more doctors. We'll have a lot more lawyers. Many more management consultants. Potentially more engineers and researchers, though those gigs require specialized graduate education -- frequently in the hard sciences -- and I'd imagine there's not too much overlap between college kids interested in organic chemistry and college kids who end up in finance at 23. (emphasis CJ's)
As a former organic chemistry graduate student, I can say that finance/ consulting are hugely popular alternatives to academia/pharmaceutical research. I think about 25% of PhD students went in to consulting from the Harvard chemistry department during the years that I was there (2005-2008) (emphasis CJ's), and McKinsey had a very strong recruiting presence, which made it seem that consulting was the main alternative to a lab based research career.