What if James Comey did not send the Comey letter on October 28, 2016?

What if on October 28, 2016, James Comey, the now former FBI Director, chose not to send a letter to Congress informing them of the reopening of the investigation into Hillary Clinton's emails? Comey's letter went against standard DOJ policy, which was not to comment on open investigations, especially before an election. Comey's conduct was seen as wrong, unpredented and reckless by many legal experts and they argued he should have not commented on the matter at least until after the election. Comey himself defended the decision saying that going through the door named 'conceal' would also have been catastrophic and the best option was to send the letter. However, the evidence shows that, despite many media denials of this(probably because if Comey cost Clinton the election, their coverage of the Comey letter could be said to have cost her the election), Comey cost Hillary Clinton the election. That's not to excuse Hillary Clinton's campaign or diminish Trump's, she made mistakes and was a flawed candidate and other factors played a role. But if Comey had not sent the letter, she likely would have been elected. The letter had a noticeable impact on the polls, and as Nate Silver said, that impact was not one of a downward trend over time but of the polls being shifted by a major news event, such as a vague letter that reopened the Clinton email investigation, with the words 'Clinton, email, FBI' being in voter's thoughts and wall-to-wall coverage of the letter, and without enough information it helped foster the impression Clinton was indeed crooked. This is proven by the majority of media coverage of Clinton in the final stretch, in contrast with previous weeks, being negative. On October 28, Clinton led Trump by 4.6%(http://www.realclearpolitics.com/epolls/2016/president/us/general_election_trump_vs_clinton-5491.html), on November 3, she led him by 1.3%. Clinton's favorability rating fell from -7% to -14% in a week, moving much closer to Trump's very low ratings and enabling him to pull off an upset. Undecided voters went to Trump, swinging Michigan, Wisconsin and Pennsylvania to him(without which he would have lost the election), all of which he won by less than 1% and perhaps swinging Florida too. While the investigation was closed just before the election, the letter misleading created the impression Clinton was corrupt, cost her early votes and there were many undecided voters, and the last thing they were hearing about was 'Clinton email FBI' and not Trump's flaws. Nate Silver also recognized that Comey cost Clinton the election(https://fivethirtyeight.com/features/the-comey-letter-probably-cost-clinton-the-election/). Most likely college-educated white voters who had voted for Romney but were undecided because of Trump(Trump did far worse with college-educated whites than any Republican in decades) 'came home' to Trump because of the letter and otherwise may have voted for Clinton. The question Silver  asks is whether the Comey effect was a 'Little Comey' effect or a "Big Comey' effect. My results for no Comey letter are more towards a big Comey effect.