A very important point, This vote for the court has a lot of bi-partisan support. So senators facing tough re-elections in 2018 need to ask what is more important, their hide or schumer's back side.
I believe the Democrats have long planned to allow their Senators who are vulnerable in 2018 (Manchin et. al.) to vote for Gorsuch but only in such numbers that Gorsuch gets 58 or 59 votes. They will force the nuclear option so that they can attempt to delegitamize the Court just as they are attempting to delegitamize Trump. They must also force the nuclear option because their activist base demands it.