He reaffirmed this when he resigned from the Shadow Cabinet. He disagrees with Corbyn's strategy on Brexit, but he doesn't want Corbyn to resign.
And you know perfectly well the PLP would never allow anyone as far to the left as Clive to be on the leadership ballot if it was left up to them.
And I've made suggestions as to how the PLP might be able to persuade Corbyn to go if he's really that much of a problem:
1)They could commit to making sure at least one other left-wing candidate was nominated in the leadership vote to replace Corbyn;
2)They could agree that all the suspensions and expulsions imposed on left-wing people during the last leadership vote being lifted, since all of those people should have a right to vote.
3)They could commit to restoring full internal party democracy.
Instead of offering anything remotely close to those proposals, they've offered nothing but a proposal to invent a pathetic, meaningless position as "party president". In that position, Jeremy would have no say in policy and would be expected to unquestioningly support the restored Blairite agenda the PLP wants to impose. And he would be expected to support every act of retribution the party imposed on his supporters.
Why would you ever expect the man to go under those circumstances? You wouldn't, if you were him.
And it's not about "purity". It's about fighting for the people. You can't do that and support the benefits cap, the budget charter, bombing Syria and Thatcher's anti-worker laws(the agenda the anti-Corbynites insist on, from all that I've read).