I saw that or a similar documentary some years ago. Also the movie with Clint Eastwood (wasn't it?). The escape is plausible, but so is drowning and disappearing at sea. The real trick after a successful escape would have been creating a new identity and remaining undetected for life. That would probably require some close coordination with the outside before the escape, while still investing tremendous energy getting out. And having the helpers maintain absolute secrecy. Again, not impossible, but a rare circumstance. I've visited Alcatraz and it is a pretty stark piece of rock with nasty currents and (I understand) seriously cold water. The wind is pretty oppressive even on a pleasant day and must be deadly in bad weather at night. Developers have coveted it, perhaps, but it's not a pleasant location, pretty harsh.