why will someone die if they have a laceration to the medulla?

Because the medulla controls all the autonomic body functions such as
respiration.  It's the "non-thinking" portion of the brain, that
controls all the basics the body needs to survive.  It's located at
the base of the brain, at the lower back part of your skull.

When you say "laceration" I am assuming a laceration serious enough to
interrupt at least one of those critical body functions.

Here's a web page with all kinds of information about the medulla
oblongata, the full name for the medulla.

http://biology.about.com/library/organs/brain/blmedulla.htm

Regards,

historybuff

search strategy:
"medulla oblongata"