The Republicans will pick up the Senate whethere Obama is re-elected or not. The Democrats just simply have too many seats to defend and too small of a majority currently.
The GOP only needs four pick-ups for 51 seats. They've already pretty much locked up three: ND, NE and MT. So that means they have to manage a pick-up somewhere between HI, NM, MO, WI, FL or VA. Maine and Massachusetts will be Republican holds. King will be elected in Maine and will caucus with the GOP and Warren does not fair to well with Massachusetts Dems outside of Harvard Yard, never mind that she will be every Super PACs number one target.
Also, even though they aren't now, I bet the races in Pennsylvania, Ohio and Michigan become more competitive as the election draws nearer. These swing states will have produce a good race.
With these factors, I do not see how any reasonable person can reject the idea of Senator McConnell being elected Majority Leader come January.
King will not caucus with Republicans. If he is, the DSCC chair wouldnt be openly supporting him. HI will not even be close with Obama on the ballot and Obama will easily carry NM. VA will go whatever way the Presidential race goes in that state as will FL.