I've had a few games that lasted all the way into high levels (or the HERO equivalent of high levels, since it's point-based), but most end within the first few adventures.
I'm making a particularly concentrated effort to keep my current campaign going as long as I can, just so I can have had a 1-20 campaign -- but it ain't easy! I keep coming up with new things I want to do instead. We're just about to break 9th on it.
Any way you define 'mid-level' my answer is no. However, the group I currently DM is approaching 9th, and I've recently vowed (to myself) to take that campaign as far as it will go.
If you've read the Story Hour, you'll realize the amount of foolishness present in that vow.
Used to be No, but times, they are a changing. As a GM, I can regularly get PCs up to 12-16 level without losing total interest in the campaign. However, as a player, the highest level I achieved in 3.X is 9th, and in 2nd edition it was 12th (paladin). All other characters fall between 2nd to 4th level.
No, pretty much exclusively not. About 9th is about as high as we tend to reach. So we get to mid-level, but I rarely to the superhero heights of high level PCs.