He is up for re-election in 2020, and he has been losing supporters in the Senate for a while now. It is almost impossible to guess what the Senate will look like by that time, but it is increasingly likely that it won’t look the way he wants it to. That leaves him with two options going forward at that point.
The first option is to start acting conservative and to have an actual legislative agenda to match. That will be tough for a moderate/centrist like McConnell, but it could be done.
The second option is to double-down and hope that the people who remain in the Senate are still loyal enough to him that they vote with him. This is even tougher, because like the Democrats, the Republicans have a base that is motivated to upend the Washington establishment, of which he is a member.