You can't die, but the penalties are cumulative.
The first time you get a "You need to drink" message (one that acctually gives the penalties) you get -1 saves (or -1 attack and damage for hunger.) The next time you get a message if you haven't eaten or drank anything you get another -1, bringing it to -2 and so on.
I know one time lal was at -4 saves because of not drinking hehe