I don't think momentum will go away and he will have difficulty uniting the party. If it's a case of mass change to appease the electorate then the perception (IMO) is a return to the centre ground and the whole reactionary process will begin all over again. The electorate tend to move either hard left of hard right - we've seen it with Trump. Essentially millions of people in the UK maybe the world are pissed off with Politicians who enmasse don't seem to be capable of doing anything apart from towing the corporate globalist line that is fucking the world up.