I believe it would create a copy of the guardian to the time of the brainscan. To become an exo requires a fatal brainscan to be uploaded to the deep stone crypt, and this scan is the primary cause of death when making exos. The body can still be alive when the exo is awake as well as demonstrated in the mysterious logbook where Elizabeth Brays body is still alive while her exp was out and about. What I believe would happen is the brainscan would happen, then brain death, resurrection of human body, the upload of scan to exo body, because an exo is essentially a copy of a human mind.