I would support the covering official stopping this play once he determined the player's safety could be in jeopardy. Obviously, as officials we want to minimize our hand in the game, at least most of us, but the alternative considering the potential impact should his helmet come off could have life consequences. Understandably, the rule states "...helmet comes completely off," however, in this situation the RB is clearly grasping his own helmet to make sure it stays on. If the RB had not reached for his own helmet, as an official, I think I would let it play out live. The indicator for me that this situation is potentially hazardous is that the RB has acknowledged there is a problem with his helmet, and from the LJ view, he can see that contact is imminent.
Additionally, I could not support an EJ for B57, I see PFFM and nothing more. B77 action, while suspect, is legal, and how do we know that the player WILL be tackled, the contact by B77 could have been a great block should the RB break loose.