Nearly 81 years after the event it's easy for us to find it incredible that so many clues were failed to be reported properly or that intelligence analysts failed to link the clues they had together to provide irrefutable evidence that the Japanese were about to go to war with Great Britain, the Dutch and the U.S.
The US had SIGINT clues, without revealing any code breaking secrets, that Japan might be about to strike U.S. assets as far east as Hawaii or Dutch harbor. Contrary to the popular notion that the Kido Butai was observing complete radio silence, John Toland in "Infamy" pp.291-294 relates how multiple very strange radio intercepts with RDF bearings were reported to USN 12th (San Francisco) and 14th (Pearl Harbor) District Headquarters but action was not taken.
On 30 November, radio operators on the SS Lurline enroute to Hawaii began to pick up and record strange Japanese transmissions northwest by west of their position coming from an area of the stormy North Pacific that was usually void of shipping that time of year. A more than 2 hour series of transmissions from JCS Yokohama was being broadcast in code that were being acknowledged by repeat back verbatim by station JOC and others somewhere in the North Pacific, "possibly for copying by crafts with small antennas." The lengthy transmissions were good enough to get RDF bearings. In 30 years, the operators had never heard JCS Yokohama broadcast before 9PM and then have the entire transmission rebroadcast on the lower marine frequency from somewhere in the Pacific. They felt the situation so unusual that they kept a detailed log to present to naval authorities when they arrived in Honolulu on 3 Dec. The next night, 1 Dec, it happened again, and again, but even stronger transmissions were recorded on 2 Dec. Something was happening, but what? (Toland, Infamy pp.291-293)
12th Naval District Intelligence (San Fransisco) was also involved in the hunt for the possibly missing Japanese carrier task force and analysts were collating reports from commercial ships and the 4 wire services. One of the wire services reported queer signals west of Hawaii on a frequency that didn't make sense. Other services and shipping companies were asked if they were getting strange signals, and several confirmed that they had. Plotting signal bearings on a large chart, they located where the bearings intersected and reported to the 12th Naval District Intelligence Chief, Captain Richard T. McCollough, that this could be a Japanese carrier force operating near Hawaii. (Toland, Infamy pp. 293-294)
Now, back to the Russian freighter: If the freighter had come under attack by Kido Butai cruisers and destroyers and had time to get off an RRRR, under attack by surface warships! and broadcast their position before being sunk...naval intelligence analysts will now have a clear picture of Kido Butai's location and hostile intent. Long range submarine and aircraft patrols could begin actively seeking the carrier force.
Even if not pinpointed and engaged in the North Pacific 4-5 days before the intended Pearl Harbor attack date, Nagumo and Japan are screwed! The surprise needed for success is gone, there is no plausible peaceful reason for the Kido Butai to have been discovered where they are, and now they've gone and sunk a neutral vessel. Nagumo will be forced to break off and return to Japan without attacking and will likely commit suicide. The sham negotiations in Washington blow up, Russia tears up its Non-Aggression Pact with Japan, public opinion goes from being isolationist to Gung Ho and the U.S. goes on a war footing.