TL;DR Its a harder road depending on who is hiring you.
Years ago, I dropped out my junior year of high school to be a junior sysadmin at webdev shop in Chicago. I was 17, had worked there for about 6 months, and summer was ending (this was around '99; right before the dotcom collapse).
I could've chosen to go back to high school, but I didn't see the point. I was learning far more in the real world. To get this job though, my boss (who I'll never forget, and to this day appreciate the chance he gave me) had to take a leap of faith. He was hiring a kid with no real work experience, no degree, no proof he knew what he was talking about besides the pictures of his breadracks in his basement with x86 machines networked and crunching through DES keys for distributed.net (which was the style at the time).
Once you get your foot in the door though, the sky is the limit. I've had the opportunity to work on some amazing products and technologies, private and academic, all because I had a few years of experience when it came time to apply at those jobs (after a few years, no one asks about your education if you know what you're doing, and if they do, you probably don't want to work there anyway).
You can most definitely use a portfolio or knowledge in lieu of a college degree. You may have to knock on more doors, you may get turned away from more places, but you'll still be able to get hired.