I know that MIT doesn't require a HS diploma, but I would be careful. If you have some great hook, then you are probably okay without the diploma. But absent national academic awards, published research, or something of equal worth, I would make sure my kid had a HS diploma.
If you are near a four year college, then you should not run out of math courses. Distance learning can also work, as well as taking courses such as AP Statistics and Linear Algebra. Absent those options, perhaps the kid can do an "independent study" project for math. There are always options.
