McConnell would need to get the entire Democratic caucus on board to expel Moore, plus 19 Republicans.
48 Democrats/Independents + Collins, Murkowski, Gardner, Flake, McCain is 53. Corker might vote to expel, perhaps even Heller which would bring it to 55 votes. Shelby came out against Moore, so that is a possible 56th vote. Toomey. Portman and Ernst are possibilities, but unreliable ones but let's add them for arguments same for 59. And if McConnell really wants him gone, that is 60 votes. Those last 7 votes are where things could get tough.
There are a bunch of low-profile, generally very conservative, leadership allies from safe states who will probably vote with McConnell if he moves to expel.