Right, but that's not what you disagreed with. I said a player who HASN'T completed the catch process would still have to maintain possession while contacting the ground -- and that's true even without item 1. You said, "No, because they're removing Item 1", and I still don't understand why you disagreed or what the removal of Item 1 has to do with it. The only real effect of removing Item 1 compared to 2011-14 is that you'd lose the language that says surviving the ground completes the catch process. Not a big problem, because you could list surviving the ground as a football move.
Very simply, once a player completes the catch process, he's a runner. So all the rules that apply to runners apply to him. If he loses the ball, it's a fumble. If contact sends him to the ground, it's a dead ball and he's down by contact. If he goes to the ground with no contact and loses the ball, it's still a live ball, so that's a fumble.