I don't know about 10 years later, but been there and done that myself over a shorter span of time. When I was in HS, my father and I got to the point where I had to leave, so I enlisted in the military. About a year later, I enrolled in night school for adults, and it seems they ordered my HS transcript from my former school. I got my diploma within 4 weeks, simply by completing what I missed.
Seems doable to me. Also, good for your friend, albeit late, for cleaning up his life.
Edit: I was only 18 years old at that time. I have been to college since then.