That report [by the Senate Research Service] also says that in the case of a tie vote the chief justice would not be expected to vote, as the vice president or another senator could when they preside, and that any tie vote during an impeachment trial defaults to the negative result.
Van Hollen’s motion would still need a majority vote to change these rules to give the chief justice more authority and avoid the long delays threatened by the president’s legal team.
Thus, it looks like, with Alexander voting against calling any more witnesses, the worst that can happen is a tie that defeats the motion and Roberts will not be able to cast a tie breaking vote.
Correction:
When I referred to a report by the “Senate Research Service” I should have referred to the “Congressional Research Service.”