Wrote a few words about this elsewhere recently:
The role of the Chief Justice in an impeachment trial is not set in stone. The procedure has been invoked so infrequently that much remains uncertain. He may decide certain questions with the advice of Senate parliamentarians, but decisions he makes can likely be over-ruled by a vote of the Senate (and the margin required for such a vote is not certain, either).
In these circumstances, it is a fair bet that a vigilant schemer such as McConnell will not be completely side-lined during an impeachment trial.