The problem with the Reverse Flash is that his time-travel shenanigans mean that you never really know when you’re dealing with him. Is this him on his first outing? Or is he already done killing everyone you know, but you managed to defeat him and fix everything and now he’s showing up for round two or fifty? He’s traveled across timelines so much that he’s effectively immortal. He’s been killed, but still shows up because the one that Barry killed was him on a different jaunt in time. There’s absolutely nothing linear about the Reverse Flash.