If their vote will be the deciding vote on anything, they'll side with the Dem leadership every time. If something will pass anyway WITHOUT their support, the Dem leadership will probably allow them to side with the Republicans, in order to increase their chances in the upcoming election. It's their way of fooling the voters into thinking they aren't under the thumb of the leadership.
Well, these dem senators are between a rock and a hard place. If they oppose the nominee, the will lose and the nominee will be approved in mid-November. I do think it’s a stretch to get ‘er done in the fall, but that may be a good thing as it will energize the Trump base and allow Trump to go on the campaign trail like he did in ND.