Nagumo rearmed at about 715 ish A.M., switched his planes from HE to torpedos and penetrating bombs. In their hurry they stacked the ordinance around the decks and hangers like firewood some sources say. Which made the US strikes 10x more damaging.
Hard to say how many of our carriers he would have caught, maybe 2 of the 3? If he would have just launched the strikes.
Speculation.
So say neither sank (how likely?) but both had shattered decks, massive fires. You would be talking of huge losses in trained personnel, US aircraft on return would find no decks to land on save one or midway which had chaos and cratered runways. So how many planes would have been lost, to ditching or wrecks, how many more pilots? Both those carriers would have been out for a long time for repairs.
Plus Hiryu likely would have survived the battle untouched (she wasn’t killed until that evening) and with aircraft from the other 3 carriers (we assume would still have been sunk—not a guarantee with ordinance being stored properly) been bursting at the seams with planes.
It’s obvious Nagumo made a massive mistake in not using HE to strike when he could. This of course is with the clarity of hindsight.
It would not be war changing but certainly affected the course of events to our detriment. Imagine the touch and go fighting we had at Guadalcanal a few months later (our most lopsided loss of the war besides midway was Savo Island) and now throw in a fully loaded and veteran crewed Hiryu lurking around “iron bottom sound”.
Things might have went much harder on us.
It’s interesting to look at the alternative paths history might have taken.
Edit
“ our most lopsided loss of the war besides midway…”
Oops meant Pearl Harbor.
Also Midway Island is never given enough credit. Although they failed to hit any targets, their continual attacks cost the Japanese valuable time to rearm and recover aircraft.