Flake has nothing to lose, unfortunately.  Or so it seems.  He decided against running for re-election, and he’s a Never Trumper.  This is his way to stick it to President Trump as he leaves the Senate.
ETA:  That assumes that McConnell doesn’t have 50 Republican votes.  If he does, he plows ahead and gets a 50-50 tie, which is broken by VP Pence.