What ifs are difficult. To assume that if Jackson had not been killed at Chancellorsville and hence had been commanding a corps at Gettysburg and later battles and that would have made a difference in the eventual outcome of the Civil War, is to assume that Jackson would never have been killed or severely wounded at any other point in the war.
It also assumes other factors, such as his Stonewall Brigade, in fact, his entire corps, would have remained mainly intact also throughout the war. It assumes that Jackson would always have been functioning at his best.
It even assumes variables such as Jefferson Davis assigning Jackson to command the Army of Tennessee to replace Joseph E. Johnston which isn't out of the realm of possibility if and only if Jackson had survived (and Lee would have allowed it.)
I do sometimes wonder, however, if Lee's thinking at Gettysburg was not at least somewhat impacted by the recent loss of his right hand man, Jackson. For example, maybe Lee lacked complete confidence in his other corps commanders, Longstreet, Hill and Ewell. Plus Lee had to deal with Ewell's recalcitrance and, of course, the untimely flare up of Hill's chronic disease. Lee surely would have been more comfortable with Jackson by his side. His absence had to have plagued Lee.
Great post. I'm not a big fan of what ifs.