Who would be splitting? I assume along with Benn goes folks like Dennis Skinner and Ken Livingstone?
Also, it was very unlikely that Kinnock and Foot could make deals with the Gang of Four. Although all of them liked Michael Foot, none of them trusted his judgement. Rodgers in particular thought Foot was a complete incompetent after several meetings with him. I don't know how prominent a role Kinnock could play either. Owen openly loathed him, while Williams and Rodgers thought he was an opportunistic lightweight. Jenkins was not even a member of Labour when the split happened and had drifted far off from Labour by that time.
The Socialist Party would never last if that was the case. There'd be no deal with the Liberals, so it would be even harder for the Socialists to keep their seats. Also, if the Gang of Three does remain in the party and Labour does move to the center, by 1992, to keep Labour as center-leftist, Denis Healey would have needed to be elected and not Michael Foot in 1980. With a split, I suspect Labour would double down and after Healey elect someone like Owen or Roy Hattersley as leader. I suspect even with that, Roy Jenkins and his closest followers like Dick Taverne and David Marquand would have joined the Liberals.