Had Jackson survived Ewell would still have commanded the new third corps in the Army of Northern Virginia. The reorganization has been planned for some time. Lee thought, quite rightly, that a two corps format led to units too big for one general to maneuver. Jackson's death did not initiate the reorg, and his survival would not have prevented it.
Ewell failed to follow up his victory of July 1, and then let the Yankees entrench on Cemetery Hill. Jackson NEVER would have made that mistake, and would have taken and secured the high ground.
That was Hill more than Ewell. Hill's corps was first in the battle. Ewell came in later in the day and engaged the Union right. Ewell's major failing was not taking Culps Hill on July 1st. And July 2nd. And July 3rd.
Ewell’s major failing was not taking Culps Hill on July 1st. And July 2nd. And July 3rd.
Ewell’s orders from Lee were discretionary. Lee never gave Ewell direct orders to take Culp’s Hill on the 1st, 2nd, or the 3rd days.
Lee would not have had Ewell command such a critical effort; he would have had Jackson command it. Remember, on July 1 Ewell’s Corps (which would have been Jackson’s had he lived) was the northernmost Confederate force, and attacked south at Howard’s force, and drove it south through the town. With Longstreet and Hill attacking from the west the Yankees should have been driven from the field and denied the high ground.
As for Culp’s Hill, Ewell sent Johnson’s division (which was part of Ewell’s corps) to invest it, and Johnson made at best only a half-hearted attempt, and Culp’s Hill remained in Yankee hands. Because Culp’s Hill was so heavily wooded it was impractical for artillery. And, while Culp’s Hill did command Cemetery Hill, which was to the west, it would not have been able to lay siege to a Confederate force there (because of the poor offerings for artillery). So, controlling Cemetery Hill would have been a far better objective than taking Culp’s Hill.
The failure to take Cemetery Hill allowed the Yankees to occupy Cemetery Ridge, as well, thus completing the formidable “fish hook” defense. Had the Confederates taken Cemetery Hill, it would have split the Yankee defense.
But, this is why history is so much interesting and fun: We get to constantly “re-strategize” and fight battles over and over again, to see how things “might have been.”