If it were just me with a victim, I'd only leave them if I were completely sure their condition was not life-threatening and I knew I could make it to help quickly. Otherwise, I'd stay with them and toot the whistle in bursts of 3 every few minutes... a prepared person could afford to stay put for a couple days, and help ought to be eminent if they left an itinerary with someone back home.

I know in my wilderness first aid class, we were told to round up whoever was available and assign them to provide first aid, give orders, find help, etc. based on who has what skills. Having 3 people to a group makes the scenarios easier; even doing something as simple as giving first aid can get tough if it's just a victim and one caregiver.