The main thing with Santos, was that while his voted was kind of needed in such a tight House, his sticking around was making it almost impossible for not just the Republi'cans' to establish a new contender for his seat, for the next election, but he was also harming the chances of the 5 other vulnerable NYS Republi'cans' in the next election.
Those are very tough seats for Republi'cans' to hold because if the Dem base gets very motivated they will take them all and Santos was being used as that motivation, by the Dems in that area.