Since I've been at college this past year, my 2006 Toyota Highlander Hybrid has been parked in my garage back home. When I went back home in December for Winter break, the car drove perfectly fine. I went home last week for Spring break only to find my car battery dead. Nobody else in the family drives it while I am away, so I am certain that no lights were anything left on in the car.
Does the battery of a hybrid car die every time you leave it for any period of time?

I'm not surprised. If I leave any of my vehicles unused for 4-5 months, the battery is usually dead when I get back. Car, motorcycle, boat. They're all the same.

Hook it up to a trickle charger that can maintain a float charge and you'll be fine.