Field, Hoey, Stringer and Mann will leave because they're about to be pushed, they are quite distinct cases unified only by the fact they were in the wrong party from day one. Expect anti-Semitism and the fashionable "toxic atmosphere" to get aired ad nauseam.
I expect the blairites to use the anti-Semite card quite a bit on the fringes and outside Labour Party conference, I gather bodyguards are being hired for a number of Jewish MPs, it's all being geared up to create a spectacle, they're praying for something to kick off and no doubt there'll be demonstrations for the camera and high profile speakers creating soundbites for the BBC and the Mail.
I don't think Field going heralds a party split, as you say he'd run out of road, the blairites will keep their powder dry waiting to see what happens at conference and the polls. Not sure where this will end up, if the blairites do take the plunge all they'll do is secure another Tory government and Brexit on Tory terms.
If Corbyn is for turning on Brexit the blairites will temporarily fall in line, without Corbyn they don't have a ground game because precious few members will pound the streets for the likes of Umunna. Of course anti-Semitism will be forgotten, they can resurrect it later once they get what they want on Brexit, assuming, that is, they do get it.
Jews using conspiracy to secretly pull the strings behind the scenes and support their favoured outcome huh?