You can send tech divers down that low. I don't know anything about these vehicles, as to whether they are water tight at that depth.
Google says they weigh 29.1 t (64,000 lb)
That's twice an aircraft carriers anchor
There are large ship cranes that could lift that.
You could also displace 64000 lbs of water = 29000 kilo = 29000 liters of water with an air bag to raise it.
states they took on water, so its probably full...
Seems they assume death given details and time:
One Marine was killed and eight others were missing after their small amphibious vehicle took on water in an exercise off Southern California.
abcnews.go.com
Terrible.