I'm somewhat intrigued that no one has asked this.
Why would not having GPS cause you to lose your Phantom? You should (and could) be able to fly your Phantom with no GPS whatsoever. I'm sorry, but blaming the loss on a lack of GPS lock is a poor excuse for losing a quad.
If you guys want to have a pity party, that's all well and good, but something else happened.
Not having GPS on the tablet did not cause the loss. Not setting a RTH before launch, them losing radio control during flight, appears to have caused the loss. If he would have had functioning GPS on the tablet, he could have set a RTH point during flight.(providing he realised he had no valid RTH point before he lost contact)
Without active GPS on the tablet, setting a new homepoint at your current location is only possible by flying your drone to your current location first.
As it was, the RTH point was not recorded before takeoff, so was likely set somewhere over the water, once the aircraft found enough satellites.
The drone either suffered some other sort of loss, like a bird attack that put it in the water, hitting one of the sailboat masts, battery falling our, motor failure, etc, etc, or, it actually returned to wherever it set it's home point, (almost for certain over the water) and landed.