Sadly, plain resurrection is much simpler and scientifically more plausible than traveling back in time.
However, time travel has the intrinsic drawback of erasing the progress you've made after a person's death, along with other limitations that I'll simply refer to as Visual Novel Sickness.
Jesus saves and makes incremental backups, that's true for people here. Using a little bit of nanomachine magic and quantum supercomputers, it becomes possible to regularly back the mind up. And if you were wondering, you can't touch those backups.
The only drawback is that progress after the latest backup will be lost. However, the worst that can come from that is that you don't remember the details of your death (that's what GoPros are for), and if you happened to mess up the timing, you might have to lose your virginity again.
So, resurrection is a guarantee in this world. You will come back like in a video game.
So, what intrinsic drawback can I place on resurrection so that death would still have the same emotional impact?
In other words, it's not arbitrarily placed there by Vecna, but is a limitation that arises from how resurrection works.
A more concrete example of intrinsic limitations: with Visual Novel Sickness, your self-insert has to protect the character you want to save and that imposes a material issue and an information issue gradually, as the timelines diverge. You can't solo an army, and you don't know what your friend will do now, since the previous minute was the last time you saw them alive. You know, standard save-scummer issues.
Unlike the Captain McKenna question, it's not necessary for the drawback here to impact anything besides the characters' emotions.