I suspect the result would have been the destruction of Nagumo's force and a very extensive American casualty list (ships, aircraft, and men).
The Tin Can Sailors, in an amazing act of courage and resolve, took on a force that was orders of magnitude more powerful. No war gamer of the time would have given then any chance at all of success. But they were incredibly successful in their mission, protecting the landing force. Their aggression and resolve so un-nerved Nagumo that he made a critical error (ordered a confusing course change for his force) which caused a complete loss of cohesion and command. The confusion caused him to think he was dealing with a MUCH more powerful force than he was and he lost his resolve. He ordered a general retirement.
Interestingly, he was also the commander of the Pearl Harbor attack force and he did the same thing when he retired vice launching a third strike. Had he done so he would have caused massive damage to the infrastructure at Pearl (dry docks, piers, POL storage, warehouses, etc.). This would have made recovery from the damage suffered at Coral Sea impossible to repair meaning the Battle of Midway might never have occurred but if it did we would have had the really short end of the stick.
Our losses of Samar were large, in ships and men, but we could afford them. And the mission they had was successful.
It's well to remember the crews of light carriers in all of this. While under fire from Japanese heavy units they continued to launch and recover aircraft who attacked the Japanese units with light bombs and rockets and strafing attacks because they had no torpedoes or armor piercing bombs. The job of the aircraft on those ships was ground support of the troops ashore and anti-ship weapons were not foremost in their inventory. Two were sunk (GAMBIER BAY and ST. LO). I don't know the number of aircraft lost.
It was an amazing event. The crews of the U.S. vessels acted in the highest and best traditions of the U.S. Navy.
SQQ