So if he can Time Travel his death does not matter. As Doctor Who has taught me. Time is only relevant when it comes to fixed events. Everything else does not matter. So if Sasuke killed Itachi, it might have been a very old Itachi he killed, maybe like when he was 100 or more. The rest of the things Itachi does is when he was younger and more powerful as he goes through time. For us it will be the present, and for Itachi the past. When Itachi died to Sasuke was actually the future...Of his timeline...
...lol