Donīt the navy pilots wear a lifejacket? actually a floating device, you can see it popped-out when hollywood and his RIO are getting off the chopper after beign shot down in the final dogfight. it's designed so it keeps your head out of the water even if you have passed-out, and inflates automatically after touching water, so Goose wouldn't have drowned while wearing it... (wow, I think I've read too much jaja, that sounded geekish... 
)
If memory serves, the explaination of Goose's demise was that he had a broken back and/or neck from impact with the canopy (something not likely to happen in real life anyway due to the way the ejection system and canopy release explosive bolts fire in different trajectories... but they took...ahem... creative license). I don't recall if they ever actually said that was the cause in the movie, but it was implied with the impact shot, and the blood coming from Goose's head when Maverick gets to him.
It seems that Dr. Greene... I mean Goose... I mean Anthony Edwards seems to get killed off fairly often in his projects.... first in Top Gun, then in E.R., and I think he buys the farm in a number of other things in his filmography background.... poor fellow!
