"Is it possible that he's letting it go to a vote because not so doing would necessitate his calling in the moving vans?"
If he's got enough votes to win (which he does), then there wouldn't be nearly enough support for any challenge to him as a result of not holding a vote.
He's only got a year and a bit left anyway, at best guess. The ongoing police investigations into donations to the Labour Party are more likely to make it shorter than anything else.
But if support was weak (or worse) within Labour,couldn't he be tossed overboard by his own Party?
I do recall Cameron having said that if it came to a vote,Blair could count on support from the Tories during Question Time a week or two ago.