Sort of. You never stay in the lunge position for long, not because you've necessarily hit or been hit, but because you almost always advance (by moving up your back leg) or retreat very quickly if you fail to hit. It is not any kind of comitted all or nothing position, in fencing, as in boxing, these are generally discouraged.
When a fencer lunges, he knows he's not going to have to fight from the vulnerable position. Either he's going to get a touch from his lunge, or he's going to get countered and his opponent will get a touch. After the touch, they'll be reset and start over. You don't see fencers (as a rule) choosing to get down into the lunge-end position and fight from there.