Corbyn is mostly untested at the polls. At the Royton by election there was a 7.3% swing to Labour. He can only be removed when he is a proven electoral failure.
There is an upcoming by election, and the London Mayoral Election and Labour will have to do very badly in those, though there is no reason to believe they will do.
Labour MPs don't want Corbyn. They are mainly Blairites parachuted into safe seats as rewards for their toadyism. They were elected on Miliband's ticket, which the country roundly rejected. Labour lost the election, but the MPs that scrapped through are saying "we don't want to change".
Corbyn is offering a change. At the moment, Labour supporters seem to like him.