I guess a highly intoxicated college girl is not alarming to a college guy such as JR and MB... but a the bruised face? I had my share of rough nights in college and many friends who were big partiers-- I never saw a girl with such an injury after a night out, and would have been alarmed if I did!
JR and MB should certainly have been concerned enough about Lauren to keep her at one of their apartments until morning. I presume that JR and/or MB would have asked Lauren why her face was bruised like that. Would love to know what her response was, if she was able to offer a coherent one. If they found out it was from a fall- even more reason for concern (assuming they know anything at all about head injuries). I experienced facial bruising around my eye(s) just once... after suffering a blow to the top of my forehead that left me with a skull fracture and a small brain bleed.
I am no doctor, but if the bruising on her face was from an impact that occurred elsewhere on the head (i.e. the bruise was a side-effect of a greater injury rather than from direct contact to that spot), then that is alarming and IMO it is likely what caused her death-- if nothing or no one else killed her first. I have known several people who have become unresponsive within hours of the injury and ultimately died due to brain injuries from a fall-- simple ones even; one tripped on the street curb and another slipped on ice.
BBM, one of the things that sticks out to me is that JR and MB were supposedly sober by that point (and supposedly MB had been sober all night...). In my experience, when someone is drunk it can be difficult to realize just how drunk someone else is (I mean in terms of 'had too much to drink' drunk, not falling down and badly bruised), but if these guys were sober shouldn't it have been even clearer to them that Lauren wasn't in the shape to walk home?
JR's story seems to be divided into two parts: Lauren was messed up, bruised and couldn't differentiate between a cellphone and ipod, but then a short time later she was able to walk without stumbling and he "let" her walk home alone.