Here's a natter fest complete with This Troper regarding Hero Antagonist.
If this troper recalls correctly, the reason Luke couldn't take Jacen out was not because he would die. Just the opposite; Jacen always died in Luke's visions. However, Luke always saw himself ending up as an Evil Overlord over the galaxy. This is likely due to two things; Luke killed Lumiya for something she didn't actually do, and Jacen had become a monster while Luke had turned a blind eye to it.
Different vision. In Jacen's vision, Luke died.
Luke was purposely projecting himself into Jacen's visions to block the fact that the Jedi were sending Jania after him instead. Also, Luke's visions showed that if he killed Jacen he would fall to the dark side, because it would be revenge for Mara not justice.
Here's a natter fest complete with This Troper regarding Hero Antagonist.