Hi Jonas,
I think it is important to remember that your DS is the same person regardless of whether or not he's tested, and regardless of how he does on the testing. Many a post on this forum has reminded me that testing is just a reflection of how someone did on a particular test, on a particular day, with a particular tester. If he does better or worse than you expected, he's still the same voraciously-reading, equation-solving kid.
Having said that, I think it's probably pretty normal to worry about either result, and have some anxious banter in your mind, like "What if he's not as smart as I think he is? What if he's off the charts? What will I do with him then...?"
As for after the testing....
I think the tests sometimes provide the first concrete-feeling evidence that your child is really "different" and that the ND class/track is probably not a good fit. Then you start the road to figuring out how to deal with those differences. How easy or hard that is depends a lot on your options and the attitudes of the school. It sounds like your principal sees that your DS is gifted and is supportive of the changes he might need. Many of us here would LOVE to be in that situation.
One thing I've seen a lot on this board is that people say to take it one year at a time. What you implement today may not be a good fit, or enough for your child next year. So, you may find that you are continually evaluating how things are working for your child, and then finding (sometimes very creative) solutions to make things work.
Well, those are my $0.02 -- not sure if that's what you were looking for. I'm sure others will chime in. It's a great group here!
Hang on for the ride. It can be challenging, but these kids definitely make life interesting!
