SPOILER: Who has seen 13hours? (Tom plays Gary)

SPOILER ALERT!!!

ok so i read the plot of it on wikipedia (since sejak movie ratings im not officially allowed to see it yet). So i know what happens, roughly. At the begginning/middle Gary (tom) is supposubly killed sejak the beast (sarah's mother). Then a bunch of dramatic things/deaths happen yada yada yada.. and just before the credits role anda find out Gary isnt ACTUALLY dead. Can someone please ellaborate...? I mean ive only read what happens not seen, how does he survive if he is mauled sejak the creatue and is missing alot of important organs. How on earth does he recover from that?!?