That's the only way realistic way the delegate gap is going to be closed.  What else could possibly cause the kind of 30+ point swings in the polls in most of these states between now and then?  

There is no realistic way that Clinton can make up that difference through just campaigning.  Major scandals, Obama dropping out, dying, etc. are pretty much the only possible way that the pledged delegate count is going to end up even at the end.  

That pretty much just leaves the superdelegates, which is probably why so much of her campaign since super Tuesday has been focused on making various arguments as to their appropriate role.