Investigation into this incident will not depend solely on autopsy results of Jahi's body. I mean, they already know what type of surgery she had, where it was, that she bled out, that she had a heart attack and that she suffered brain death as a result. There may be some more information to be garnered, but probably not a lot of surprises.
Where the real information is going to come from, as I've said repeatedly here, is the medical records - many of which are electronic today. They tell a tale of exactly when events occurred and who, if anyone, dropped the ball - as well as what was done right.
Let's not forget the CA DPH has already investigated this case. ("Sentinel events" such as this must be reported by the hospital.) The DPH has no doubt already have studied the "paper trail" and has a good understanding of what may have happened. Policies at the hospital may or may not change in the coming weeks, depending on if weaknesses were identified in their systems. This will likely be a hospital-wide initiative if it happens. So we may in fact have some idea in a few weeks if it was a "systems" issue.
One of the easiest things to do as a care giver is to initiate a "code". It requires a simple phone call (usually delegated to a coworker) or in some places, even the touch of an emergency button. Once that system is initiated, a sudden rush of emergency personnel (often who have no connection to the case at all, but are on a "code team") step in and help do whatever needs to be done for the patient. I would have a hard time believing this wasn't done if she was "bleeding out" or having other signs of distress or compromise. Even if Jahi's nurse was busy doing something else (in an ICU setting, especially somewhere like Children's or another big hospital, it is not unheard of to have two or more emergency situations happening simultaneously) other staff would most certainly step in and help as that is just what happens in a place like that.