If I could offer my own experience, I had a similar situation my junior year of highschool. I chose to stay for my senior year. At that point, there was no academic reason for me to stay in school, so I had actually loaded myself up with courses from a particular teacher simply so I could spend more time with him in classes (he was our schools CS teacher, so although I was in classes ranging from AP Comp Sci to Math for Seniors II [low level math], I spent my time being mentored in comp sci). I also spent alot of time in the art room. Otherwise, I had only been in that school district for about 2 years, so I did not have many relationships with any of the other students.

Basically, I think what was positive about my experience was that I was able to spend time with an experienced programmer (he unfortunately left the following year, but he had years of experience building businesses and had a doctorate in CS, so it was pretty awesome). But honestly, if that teacher was not there, it would have been a total waste of my time. Highschool sucked for my social experience, and it was mainly in college that I felt I found my place amongst my peers. Freshman year in college was pretty much that same as highschool regarding the people (and I went to a tiny private tech school), but as I got into the later years, it was definitely easier to find people that I wanted to surround myself with (motivated, smart people). The courses were hit or miss, some were really great, others were a waste of time, but unlike highschool, these courses were usually only for an hour a week. And of course, there's tons of organizations and clubs to join, whether it's with the school or the town the college is in.

So really, if there's something you think you wouldn't want to miss out in a last year in highschool, whether it is building a relationship with someone/some group of people, or taking some particular classes, I'd stay. But if there's nothing there for you, move on. You'll spend the year bored and annoyed that you are wasting 6 hours of the day essentially locked up in a building, when in college, you'll be able to go on to more interesting things in a less restricted setting. Or if you take the year off, you'll have free time to do whatever projects you want to, or go to random places.

Good luck with whatever you decide ;D