Joining Labour wouldn't be a sea change for him and would provide him with a much better chance of minister position;
Not necessarily - see my third point
He's changed party before and he'd probably do it again.
Looking at the chances of the LibDems come 2015, they certainly won't be in government either as a party or in coalition with Labour.
Well they obviously won't win a majority, so I'm not sure why you mentioned that. And it is perfectly believable, perhaps even probable, that the Lib Dems could end up in coalition with Labour if there is a hung parliament