If Jackson had survived, the first thing that would have happened would have been a victory at Gettysburg. Unlike Early, Jackson would have immediately occupied the high ground, and the battle would have been a replay of Marye’s Heights.
The first book of the trilogy </i>Throw Away the Scabbard</i> looks at that very question, but answers with Jackson’s invasion plan from the winter of 1861 and 1862.
Depends. Lee had plans to divide the army into three corps long before Jackson died, so it's impossible to say that it would have been Jackson coming in from the North. Ewell could still have approached from that direction and Jackson could have been coming in from the west, as Hill did. Or it could have been Longstreet coming in from the west and Jackson not arriving until day 2. You never know.
And if that had happened, Gettysburg would have been another minor battle of the campaign. The US Army would have found better ground, maybe at Pipe Creek, where they'd already surveyed defensive positions. Lee was going to have to attack at some point--the US Army was between him and Virginia.