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

SPOILER ALERT!!!

ok so i read the plot of it on wikipedia (since 由 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 由 the beast (sarah's mother). Then a bunch of dramatic things/deaths happen yada yada yada.. and just before the credits role 你 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 由 the creatue and is missing alot of important organs. How on earth does he recover from that?!?