I believe that our guardian was meant to die while fighting the final battle against the witness. This seems evident by the fact that ergo sum or the sword of the traveler, was present on our grave in the corridor of time.
Now consider the vex cannot predict paracausality, meaning they wouldn't have known that Crow would wish Cayde back to life with an Ahemkara wish.
I purpose that by bringing Cayde back, Crow accidentally changed the outcome as well as the events of the final shape. The most noticeable change would have been the loss of our ghost since cayde brought it back. It's also entirely possible that without cayde, the vanguard would have fallen to the witness, thereby not being able to cover our escape once we wounded him.
Just my thoughts.
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I think Crow inadvertently changed our Fate in Excision. Ergo Sum is only available after the final mission of the campaign. If I remember correctly, I believe the Ergo Sum is a sword given to us by the Traveler. A weapon made for the Travelers Chosen. Thus why it’s on our grave. I think our Guardian did die, and we were transported into the final resting place of all guardians and ghost. The same place that Cayde was pulled from, but in our final battle, we didn’t just kill our ghost. We destroyed its very essence. There is no escape of light when our Ghost dies, which is common when we see Ghosts get destroyed, like the explosion from Sundance. There was no light in our ghost to return to the traveler, and thus, we ask the Traveler to restore our ghost, not understanding that we ourselves died. It’s not until Cayde revives our Ghost, returning to the light himself, that we are also resurrected.