RQ, I will have a go at your questions
If he wins, and as you say all the adverse publicity from Right wing press and also Labour big guns,will no doubt help towards that,( although it's not a done deal yet) I think he will have problems forming a shadow cabinet( it will have to be done though!)
I don't think that the party will split up, if he wins, or if he loses.
His ideals are going back to the roots of the Labour movement( and then some) and yes, the world ,or our country and quite a few others have moved on since then, and yes if he ever became PM ( highly unlikely) I do think his ideas may well be damaging to our relationship with other countries both in Europ and the US.
Of course, I am not a Socialist, so no doubt there will be other, and differing answers.