In this case the party members are the relevant electorate though. The problem seems to be that the party members and the elected MPs are at odds since nobody actually knows what the wider electorate feels on the issue. Corbyn hasn't yet faced the electorate.
The received wisdom that the country doesn't want Corbyn seems to be based on pretty much nothing more than internal dissent from his MPs. Its entirely possible that these MPs are incorrect.
Not really, his lame performance during the Brexit campaign give plenty of reason to doubt him. There is also the facts of his stance on the IRA and the Falklands that are bound to incense a huge number of voters once the media starts shouting about them during an election campaign.
Also the man is supposed to lead the Labour party in parliament on a day to day basis, that he has lost the confidence of three-quarters of his MPs, and they have actually gone public with their discontent speaks volumes about his leadership skills.