Umm, not to be callous or anything, but being able to smile, doesn't necessarily mean he has any idea what's going on, or will regain any particular level of function at all.
The above mentioned "locked-in syndromes" are usually a result of fairly specific brain damage, caused for example by trauma or stroke.
Hypoxic brain injury, what you refer to as his brain without oxygen, most often results in global damage, which is most often catastrophic. Think not of it as your friend being trapped behind some array of disability, he's quite simply not the same person any more.
Of course, it's impossible to give any particular comment without a great deal of further info, but just my 2c as an intensive care registrar.